diff --git a/backend/migrations/018_parent_task_id.sql b/backend/migrations/018_parent_task_id.sql
new file mode 100644
index 0000000..474aae4
--- /dev/null
+++ b/backend/migrations/018_parent_task_id.sql
@@ -0,0 +1,12 @@
+-- AP1.5d: Rekursive Tasks unter Action
+
+ALTER TABLE tasks
+    ADD COLUMN IF NOT EXISTS parent_task_id UUID NULL
+        REFERENCES tasks (id) ON DELETE CASCADE;
+
+CREATE INDEX IF NOT EXISTS idx_tasks_parent
+    ON tasks (tenant_id, parent_task_id)
+    WHERE parent_task_id IS NOT NULL;
+
+CREATE INDEX IF NOT EXISTS idx_tasks_action_parent
+    ON tasks (tenant_id, action_id, parent_task_id);
diff --git a/backend/routers/actions.py b/backend/routers/actions.py
index d908fe3..e68b246 100644
--- a/backend/routers/actions.py
+++ b/backend/routers/actions.py
@@ -35,6 +35,7 @@ class TaskCreateRequest(BaseModel):
     title: str = Field(min_length=1, max_length=255)
     description: str = ""
     status: Literal["open", "in_progress", "done", "discarded"] = "open"
+    parent_task_id: Optional[str] = None
     roadmap_item_id: Optional[str] = None
     sort_order: int = 0
     due_at: Optional[str] = None
@@ -87,6 +88,7 @@ def create_action_task(
             title=body.title,
             description=body.description,
             status=body.status,
+            parent_task_id=body.parent_task_id,
             roadmap_item_id=body.roadmap_item_id,
             sort_order=body.sort_order,
             due_at=due_at,
diff --git a/backend/routers/tasks.py b/backend/routers/tasks.py
index af27c5f..13c6e9f 100644
--- a/backend/routers/tasks.py
+++ b/backend/routers/tasks.py
@@ -18,6 +18,8 @@ class TaskUpdateRequest(BaseModel):
     title: Optional[str] = Field(default=None, min_length=1, max_length=255)
     description: Optional[str] = None
     status: Optional[Literal["open", "in_progress", "done", "discarded"]] = None
+    parent_task_id: Optional[str] = None
+    clear_parent_task: bool = False
     roadmap_item_id: Optional[str] = None
     clear_roadmap_item: bool = False
     sort_order: Optional[int] = None
@@ -45,6 +47,8 @@ def update_task(
             title=body.title,
             description=body.description,
             status=body.status,
+            parent_task_id=body.parent_task_id,
+            clear_parent_task=body.clear_parent_task,
             roadmap_item_id=body.roadmap_item_id,
             clear_roadmap_item=body.clear_roadmap_item,
             sort_order=body.sort_order,
@@ -63,7 +67,11 @@ def delete_task(
     task_id: str,
     ctx: TenantContext = Depends(require_capability("kairo.action.manage")),
 ):
-    if not task_service.delete_task(
-        tenant_id=ctx.tenant_id, task_id=task_id, user_id=ctx.user_id
-    ):
+    try:
+        deleted = task_service.delete_task(
+            tenant_id=ctx.tenant_id, task_id=task_id, user_id=ctx.user_id
+        )
+    except ValueError as exc:
+        raise HTTPException(status_code=400, detail=str(exc)) from exc
+    if not deleted:
         raise HTTPException(status_code=404, detail="Task nicht gefunden")
diff --git a/backend/services/tasks.py b/backend/services/tasks.py
index a296b64..f07e8bd 100644
--- a/backend/services/tasks.py
+++ b/backend/services/tasks.py
@@ -1,4 +1,4 @@
-"""Task service — kleinste Einheit unter Action (AP1.5)."""
+"""Task service — kleinste Einheit unter Action (AP1.5, AP1.5d rekursiv)."""
 
 from __future__ import annotations
 
@@ -13,16 +13,18 @@ from services.audit import log_audit
 
 TaskStatus = Literal["open", "in_progress", "done", "discarded"]
 TASK_STATUSES = frozenset({"open", "in_progress", "done", "discarded"})
+TERMINAL_TASK_STATUSES = frozenset({"done", "discarded"})
+MAX_TASK_DEPTH = 10
 
 _TASK_COLUMNS = """
-    id, tenant_id, action_id, title, description, status,
+    id, tenant_id, action_id, parent_task_id, title, description, status,
     roadmap_item_id, sort_order, due_at, created_at, updated_at
 """
 
 
 def _serialize_row(row: dict[str, Any]) -> dict[str, Any]:
     result = dict(row)
-    for key in ("id", "tenant_id", "action_id", "roadmap_item_id"):
+    for key in ("id", "tenant_id", "action_id", "parent_task_id", "roadmap_item_id"):
         if result.get(key):
             result[key] = str(result[key])
     if result.get("due_at"):
@@ -62,6 +64,142 @@ def _validate_roadmap_item_for_action(
         raise ValueError("Gate gehört nicht zum Vorhaben des Arbeitspakets")
 
 
+def _load_action_task_maps(
+    cur, *, tenant_id: str, action_id: str
+) -> tuple[dict[str, dict[str, Any]], dict[str, list[str]]]:
+    cur.execute(
+        f"""
+        SELECT {_TASK_COLUMNS}
+        FROM tasks
+        WHERE tenant_id = %s AND action_id = %s
+        """,
+        (tenant_id, action_id),
+    )
+    rows = [dict(r) for r in cur.fetchall()]
+    by_id = {str(r["id"]): r for r in rows}
+    by_parent: dict[str, list[str]] = {}
+    for row in rows:
+        parent_id = row.get("parent_task_id")
+        if parent_id:
+            by_parent.setdefault(str(parent_id), []).append(str(row["id"]))
+    return by_id, by_parent
+
+
+def _collect_descendant_ids(task_id: str, by_parent: dict[str, list[str]]) -> set[str]:
+    result: set[str] = set()
+    stack = list(by_parent.get(task_id, []))
+    while stack:
+        child_id = stack.pop()
+        if child_id in result:
+            continue
+        result.add(child_id)
+        stack.extend(by_parent.get(child_id, []))
+    return result
+
+
+def _task_depth_from_map(
+    task_id: str,
+    by_id: dict[str, dict[str, Any]],
+    memo: dict[str, int],
+) -> int:
+    if task_id in memo:
+        return memo[task_id]
+    row = by_id.get(task_id)
+    if not row or not row.get("parent_task_id"):
+        memo[task_id] = 1
+        return 1
+    parent_id = str(row["parent_task_id"])
+    depth = 1 + _task_depth_from_map(parent_id, by_id, memo)
+    memo[task_id] = depth
+    return depth
+
+
+def _subtree_height(task_id: str, by_parent: dict[str, list[str]]) -> int:
+    children = by_parent.get(task_id, [])
+    if not children:
+        return 1
+    return 1 + max(_subtree_height(child_id, by_parent) for child_id in children)
+
+
+def _validate_parent_task(
+    cur,
+    *,
+    tenant_id: str,
+    action_id: str,
+    task_id: Optional[str],
+    parent_task_id: Optional[str],
+) -> None:
+    if not parent_task_id:
+        return
+    if task_id and parent_task_id == task_id:
+        raise ValueError("Task kann nicht sein eigener Parent sein")
+
+    cur.execute(
+        f"""
+        SELECT {_TASK_COLUMNS}
+        FROM tasks
+        WHERE id = %s AND tenant_id = %s AND action_id = %s
+        """,
+        (parent_task_id, tenant_id, action_id),
+    )
+    parent = cur.fetchone()
+    if not parent:
+        raise ValueError("Parent-Task gehört nicht zu diesem Arbeitspaket")
+
+    by_id, by_parent = _load_action_task_maps(cur, tenant_id=tenant_id, action_id=action_id)
+    if task_id:
+        descendants = _collect_descendant_ids(task_id, by_parent)
+        if parent_task_id in descendants:
+            raise ValueError("Zyklus: Parent darf kein Nachfahr sein")
+
+    memo: dict[str, int] = {}
+    parent_depth = _task_depth_from_map(parent_task_id, by_id, memo)
+    subtree_height = _subtree_height(task_id, by_parent) if task_id else 1
+    if parent_depth + subtree_height > MAX_TASK_DEPTH:
+        raise ValueError(f"Maximale Task-Tiefe ({MAX_TASK_DEPTH}) würde überschritten")
+
+
+def _has_open_children(cur, *, tenant_id: str, task_id: str) -> bool:
+    cur.execute(
+        """
+        SELECT 1 FROM tasks
+        WHERE tenant_id = %s AND parent_task_id = %s
+          AND status NOT IN ('done', 'discarded')
+        LIMIT 1
+        """,
+        (tenant_id, task_id),
+    )
+    return cur.fetchone() is not None
+
+
+def _rollup_parent_status(cur, *, tenant_id: str, parent_task_id: str) -> None:
+    cur.execute(
+        """
+        SELECT status FROM tasks
+        WHERE tenant_id = %s AND parent_task_id = %s
+        """,
+        (tenant_id, parent_task_id),
+    )
+    child_statuses = [row[0] for row in cur.fetchall()]
+    if not child_statuses:
+        return
+    if any(status not in TERMINAL_TASK_STATUSES for status in child_statuses):
+        return
+
+    cur.execute(
+        """
+        UPDATE tasks
+        SET status = 'done', updated_at = NOW()
+        WHERE id = %s AND tenant_id = %s AND status NOT IN ('done', 'discarded')
+        RETURNING parent_task_id
+        """,
+        (parent_task_id, tenant_id),
+    )
+    row = cur.fetchone()
+    if row and row[0]:
+        _rollup_parent_status(cur, tenant_id=tenant_id, parent_task_id=str(row[0]))
+
+
 def create_task(
     *,
     tenant_id: str,
@@ -69,6 +207,7 @@ def create_task(
     title: str,
     description: str = "",
     status: TaskStatus = "open",
+    parent_task_id: Optional[str] = None,
     roadmap_item_id: Optional[str] = None,
     sort_order: int = 0,
     due_at: Optional[datetime] = None,
@@ -83,6 +222,13 @@ def create_task(
     conn = get_connection()
     try:
         with conn.cursor(cursor_factory=RealDictCursor) as cur:
+            _validate_parent_task(
+                cur,
+                tenant_id=tenant_id,
+                action_id=action_id,
+                task_id=None,
+                parent_task_id=parent_task_id,
+            )
             _validate_roadmap_item_for_action(
                 cur,
                 tenant_id=tenant_id,
@@ -92,15 +238,16 @@ def create_task(
             cur.execute(
                 f"""
                 INSERT INTO tasks (
-                    tenant_id, action_id, title, description, status,
+                    tenant_id, action_id, parent_task_id, title, description, status,
                     roadmap_item_id, sort_order, due_at
                 )
-                VALUES (%s, %s, %s, %s, %s, %s, %s, %s)
+                VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s)
                 RETURNING {_TASK_COLUMNS}
                 """,
                 (
                     tenant_id,
                     action_id,
+                    parent_task_id,
                     title,
                     description,
                     status,
@@ -118,7 +265,12 @@ def create_task(
         "task.created",
         user_id=user_id,
         tenant_id=tenant_id,
-        details={"task_id": row["id"], "action_id": action_id, "title": title},
+        details={
+            "task_id": row["id"],
+            "action_id": action_id,
+            "title": title,
+            "parent_task_id": parent_task_id,
+        },
     )
     return row
 
@@ -164,6 +316,8 @@ def update_task(
     title: Optional[str] = None,
     description: Optional[str] = None,
     status: Optional[TaskStatus] = None,
+    parent_task_id: Optional[str] = None,
+    clear_parent_task: bool = False,
     roadmap_item_id: Optional[str] = None,
     clear_roadmap_item: bool = False,
     sort_order: Optional[int] = None,
@@ -189,22 +343,14 @@ def update_task(
         params.append(description)
     if status is not None:
         _validate_status(status)
-        updates.append("status = %s")
-        params.append(status)
+    if clear_parent_task:
+        updates.append("parent_task_id = NULL")
+    elif parent_task_id is not None:
+        updates.append("parent_task_id = %s")
+        params.append(parent_task_id)
     if clear_roadmap_item:
         updates.append("roadmap_item_id = NULL")
     elif roadmap_item_id is not None:
-        conn = get_connection()
-        try:
-            with conn.cursor() as cur:
-                _validate_roadmap_item_for_action(
-                    cur,
-                    tenant_id=tenant_id,
-                    initiative_id=action["initiative_id"],
-                    roadmap_item_id=roadmap_item_id,
-                )
-        finally:
-            conn.close()
         updates.append("roadmap_item_id = %s")
         params.append(roadmap_item_id)
     if sort_order is not None:
@@ -216,15 +362,39 @@ def update_task(
         updates.append("due_at = %s")
         params.append(due_at)
 
-    if not updates:
-        return existing
-
-    updates.append("updated_at = NOW()")
-    params.extend([task_id, tenant_id])
-
     conn = get_connection()
     try:
         with conn.cursor(cursor_factory=RealDictCursor) as cur:
+            if parent_task_id is not None and not clear_parent_task:
+                _validate_parent_task(
+                    cur,
+                    tenant_id=tenant_id,
+                    action_id=existing["action_id"],
+                    task_id=task_id,
+                    parent_task_id=parent_task_id,
+                )
+            if roadmap_item_id is not None and not clear_roadmap_item:
+                _validate_roadmap_item_for_action(
+                    cur,
+                    tenant_id=tenant_id,
+                    initiative_id=action["initiative_id"],
+                    roadmap_item_id=roadmap_item_id,
+                )
+            if status is not None:
+                if status == "done" and _has_open_children(
+                    cur, tenant_id=tenant_id, task_id=task_id
+                ):
+                    raise ValueError(
+                        "Task kann nicht abgeschlossen werden — offene Unteraufgaben vorhanden"
+                    )
+                updates.append("status = %s")
+                params.append(status)
+
+            if not updates:
+                return existing
+
+            updates.append("updated_at = NOW()")
+            params.extend([task_id, tenant_id])
             cur.execute(
                 f"""
                 UPDATE tasks SET {", ".join(updates)}
@@ -237,6 +407,13 @@ def update_task(
             if not row:
                 return None
             result = _serialize_row(dict(row))
+
+            if status == "done" and result.get("parent_task_id"):
+                _rollup_parent_status(
+                    cur,
+                    tenant_id=tenant_id,
+                    parent_task_id=str(result["parent_task_id"]),
+                )
         conn.commit()
     finally:
         conn.close()
@@ -247,13 +424,25 @@ def update_task(
         tenant_id=tenant_id,
         details={"task_id": task_id},
     )
-    return result
+    return get_task(tenant_id=tenant_id, task_id=task_id)
 
 
 def delete_task(*, tenant_id: str, task_id: str, user_id: Optional[str] = None) -> bool:
     conn = get_connection()
     try:
         with conn.cursor() as cur:
+            cur.execute(
+                """
+                SELECT 1 FROM tasks
+                WHERE parent_task_id = %s AND tenant_id = %s
+                LIMIT 1
+                """,
+                (task_id, tenant_id),
+            )
+            if cur.fetchone():
+                raise ValueError(
+                    "Task hat Unteraufgaben — zuerst löschen oder verschieben"
+                )
             cur.execute(
                 "DELETE FROM tasks WHERE id = %s AND tenant_id = %s RETURNING id",
                 (task_id, tenant_id),
diff --git a/backend/tests/test_ap15d_recursive_tasks.py b/backend/tests/test_ap15d_recursive_tasks.py
new file mode 100644
index 0000000..8aff849
--- /dev/null
+++ b/backend/tests/test_ap15d_recursive_tasks.py
@@ -0,0 +1,108 @@
+"""Rekursive Tasks (AP1.5d)."""
+
+from __future__ import annotations
+
+from tests.factories import provision_user_in_tenant
+from tests.test_initiatives_actions import _auth, _create_initiative, _login
+
+
+def _create_action(client, token, initiative_id, title="AP Alpha"):
+    res = client.post(
+        f"/api/initiatives/{initiative_id}/actions",
+        json={"title": title},
+        headers=_auth(token),
+    )
+    assert res.status_code == 201
+    return res.json()
+
+
+def _create_task(client, token, action_id, **payload):
+    return client.post(
+        f"/api/actions/{action_id}/tasks",
+        json=payload,
+        headers=_auth(token),
+    )
+
+
+def test_nested_tasks_and_rollup(client):
+    user = provision_user_in_tenant(tenant_role="member")
+    token = _login(client, user)
+    initiative = _create_initiative(client, token, title="Task Tree").json()
+    action = _create_action(client, token, initiative["id"])
+
+    parent = _create_task(client, token, action["id"], title="Parent").json()
+    child = _create_task(
+        client,
+        token,
+        action["id"],
+        title="Child",
+        parent_task_id=parent["id"],
+    )
+    assert child.status_code == 201
+    child_id = child.json()["id"]
+
+    blocked = client.patch(
+        f"/api/tasks/{parent['id']}",
+        json={"status": "done"},
+        headers=_auth(token),
+    )
+    assert blocked.status_code == 400
+
+    done_child = client.patch(
+        f"/api/tasks/{child_id}",
+        json={"status": "done"},
+        headers=_auth(token),
+    )
+    assert done_child.status_code == 200
+
+    parent_after = client.get(
+        f"/api/actions/{action['id']}/tasks",
+        headers=_auth(token),
+    ).json()
+    parent_row = next(item for item in parent_after if item["id"] == parent["id"])
+    assert parent_row["status"] == "done"
+
+
+def test_task_cycle_rejected(client):
+    user = provision_user_in_tenant(tenant_role="member")
+    token = _login(client, user)
+    initiative = _create_initiative(client, token, title="Cycle").json()
+    action = _create_action(client, token, initiative["id"])
+
+    a = _create_task(client, token, action["id"], title="A").json()
+    b = _create_task(
+        client,
+        token,
+        action["id"],
+        title="B",
+        parent_task_id=a["id"],
+    ).json()
+
+    res = client.patch(
+        f"/api/tasks/{a['id']}",
+        json={"parent_task_id": b["id"]},
+        headers=_auth(token),
+    )
+    assert res.status_code == 400
+
+
+def test_delete_task_with_children_rejected(client):
+    user = provision_user_in_tenant(tenant_role="member")
+    token = _login(client, user)
+    initiative = _create_initiative(client, token, title="Delete Guard").json()
+    action = _create_action(client, token, initiative["id"])
+
+    parent = _create_task(client, token, action["id"], title="Parent").json()
+    _create_task(
+        client,
+        token,
+        action["id"],
+        title="Child",
+        parent_task_id=parent["id"],
+    )
+
+    res = client.delete(
+        f"/api/tasks/{parent['id']}",
+        headers=_auth(token),
+    )
+    assert res.status_code == 400
diff --git a/backend/version.py b/backend/version.py
index efad8a3..3db984c 100644
--- a/backend/version.py
+++ b/backend/version.py
@@ -1,3 +1,3 @@
-APP_VERSION = "0.17.0-ap1.10c"
-DB_SCHEMA_VERSION = "017"
+APP_VERSION = "0.17.0-ap1.5d"
+DB_SCHEMA_VERSION = "018"
 APP_NAME = "jinkendo-kairo"
diff --git a/frontend/package.json b/frontend/package.json
index 567f095..a02683f 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -1,6 +1,6 @@
 {
   "name": "kairo-jinkendo-frontend",
-  "version": "0.17.0-ap1.10c",
+  "version": "0.17.0-ap1.5d",
   "private": true,
   "type": "module",
   "scripts": {
diff --git a/frontend/src/components/ActionTaskPanel.jsx b/frontend/src/components/ActionTaskPanel.jsx
new file mode 100644
index 0000000..0f180bf
--- /dev/null
+++ b/frontend/src/components/ActionTaskPanel.jsx
@@ -0,0 +1,194 @@
+import { useEffect, useMemo, useState } from 'react'
+import {
+  createActionTask,
+  deleteTask,
+  listActionTasks,
+  updateTask,
+} from '../api/tasks.js'
+import { buildTasksByParent } from '../utils/taskTree.js'
+import { Modal } from './Modal.jsx'
+import { TaskForm, TaskTreeNodes } from './TaskForm.jsx'
+
+export function ActionTaskPanel({
+  actionId,
+  roadmapItems,
+  canManage,
+  expanded,
+  onToggle,
+  openTaskCount,
+}) {
+  const [tasks, setTasks] = useState([])
+  const [loading, setLoading] = useState(false)
+  const [error, setError] = useState(null)
+  const [busy, setBusy] = useState(false)
+  const [modal, setModal] = useState(null)
+  const [reloadKey, setReloadKey] = useState(0)
+
+  useEffect(() => {
+    if (!expanded || !actionId) return undefined
+    let cancelled = false
+    setLoading(true)
+    setError(null)
+    listActionTasks(actionId)
+      .then((data) => {
+        if (!cancelled) setTasks(data)
+      })
+      .catch((err) => {
+        if (!cancelled) setError(err.message)
+      })
+      .finally(() => {
+        if (!cancelled) setLoading(false)
+      })
+    return () => {
+      cancelled = true
+    }
+  }, [expanded, actionId, reloadKey])
+
+  const tasksByParent = useMemo(() => buildTasksByParent(tasks), [tasks])
+
+  async function reload() {
+    setReloadKey((value) => value + 1)
+  }
+
+  async function handleCreate(payload) {
+    setBusy(true)
+    setError(null)
+    try {
+      await createActionTask(actionId, payload)
+      setModal(null)
+      await reload()
+    } catch (err) {
+      setError(err.message)
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  async function handleUpdate(taskId, payload) {
+    setBusy(true)
+    setError(null)
+    try {
+      await updateTask(taskId, payload)
+      setModal(null)
+      await reload()
+    } catch (err) {
+      setError(err.message)
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  async function handleStatus(taskId, status) {
+    setBusy(true)
+    setError(null)
+    try {
+      await updateTask(taskId, { status })
+      await reload()
+    } catch (err) {
+      setError(err.message)
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  async function handleDelete(taskId) {
+    setBusy(true)
+    setError(null)
+    try {
+      await deleteTask(taskId)
+      await reload()
+    } catch (err) {
+      setError(err.message)
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  const taskLabel = openTaskCount != null ? ` (${openTaskCount} offen)` : ''
+
+  return (
+    <div className="action-task-panel">
+      <button
+        type="button"
+        className="action-task-panel__toggle"
+        onClick={onToggle}
+        aria-expanded={expanded}
+      >
+        {expanded ? '▾' : '▸'} Aufgaben{taskLabel}
+      </button>
+
+      {expanded && (
+        <div className="action-task-panel__body">
+          {error && <p className="error">{error}</p>}
+          {loading && <p className="muted">Aufgaben werden geladen …</p>}
+          {!loading && tasks.length === 0 && (
+            <p className="muted">Noch keine Aufgaben für dieses Arbeitspaket.</p>
+          )}
+          {!loading && tasks.length > 0 && (
+            <TaskTreeNodes
+              tasksByParent={tasksByParent}
+              roadmapItems={roadmapItems}
+              canManage={canManage}
+              busy={busy}
+              onEdit={(task) => setModal({ mode: 'edit', task, key: task.id })}
+              onAddSubtask={(task) =>
+                setModal({
+                  mode: 'create',
+                  parentTaskId: task.id,
+                  parentLabel: task.title,
+                  key: `sub-${task.id}`,
+                })
+              }
+              onStatusChange={handleStatus}
+              onDelete={handleDelete}
+            />
+          )}
+          {canManage && (
+            <button
+              type="button"
+              className="btn btn-secondary btn-sm action-task-panel__add"
+              disabled={busy}
+              onClick={() => setModal({ mode: 'create', key: 'root' })}
+            >
+              Aufgabe hinzufügen
+            </button>
+          )}
+        </div>
+      )}
+
+      <Modal
+        open={Boolean(modal)}
+        title={
+          modal?.mode === 'edit'
+            ? 'Aufgabe bearbeiten'
+            : modal?.parentLabel
+              ? 'Unteraufgabe anlegen'
+              : 'Aufgabe anlegen'
+        }
+        onClose={() => setModal(null)}
+      >
+        {modal?.mode === 'edit' ? (
+          <TaskForm
+            initial={modal.task}
+            roadmapItems={roadmapItems}
+            onSubmit={(payload) => handleUpdate(modal.task.id, payload)}
+            onCancel={() => setModal(null)}
+            busy={busy}
+          />
+        ) : (
+          modal && (
+            <TaskForm
+              parentTaskId={modal.parentTaskId}
+              parentLabel={modal.parentLabel}
+              roadmapItems={roadmapItems}
+              onSubmit={handleCreate}
+              onCancel={() => setModal(null)}
+              busy={busy}
+              submitLabel="Anlegen"
+            />
+          )
+        )}
+      </Modal>
+    </div>
+  )
+}
diff --git a/frontend/src/components/PlanActionsSection.jsx b/frontend/src/components/PlanActionsSection.jsx
index ec02c9f..6379b8f 100644
--- a/frontend/src/components/PlanActionsSection.jsx
+++ b/frontend/src/components/PlanActionsSection.jsx
@@ -5,6 +5,7 @@ import { StatusBadge } from './StatusBadge.jsx'
 import { PriorityBadge } from './PriorityBadge.jsx'
 import { Modal } from './Modal.jsx'
 import { ActionForm } from './ActionForm.jsx'
+import { ActionTaskPanel } from './ActionTaskPanel.jsx'
 import { gateTitleById } from './GateSelect.jsx'
 import { buildProjectPath, collectProjectSubtreeIds } from '../utils/projectTree.js'
 import { actionPath } from '../utils/routes.js'
@@ -32,6 +33,7 @@ export function PlanActionsSection({
   busy,
 }) {
   const [showCreate, setShowCreate] = useState(false)
+  const [expandedActions, setExpandedActions] = useState(() => new Set())
 
   const visibleActions = useMemo(() => {
     let list = hideDone
@@ -60,14 +62,22 @@ export function PlanActionsSection({
     setShowCreate(false)
   }
 
+  function toggleActionTasks(actionId) {
+    setExpandedActions((prev) => {
+      const next = new Set(prev)
+      if (next.has(actionId)) next.delete(actionId)
+      else next.add(actionId)
+      return next
+    })
+  }
+
   return (
     <section className="card plan-actions-section">
       <div className="section-header">
         <div>
           <h2>Arbeit</h2>
           <p className="section-lead muted">
-            Committete Arbeitspakete im Plan-Kontext — Detail und Ausführung über die
-            Objektseite.
+            Committete Arbeitspakete und zugehörige Aufgaben — Ausführung über die Objektseite.
           </p>
         </div>
         <div className="section-actions">
@@ -104,29 +114,38 @@ export function PlanActionsSection({
       <ul className="item-list plan-actions-list">
         {visibleActions.map((action) => (
           <li key={action.id} className="list-item card-list-item plan-actions-list__item">
-            <div className="list-item-main">
-              <Link to={actionPath(action.id)} className="plan-actions-list__title">
-                <strong>{action.title}</strong>
-              </Link>
-              <p className="list-item-sub muted">
-                {formatProjectContext(projects, action.project_id)}
-              </p>
-              {action.roadmap_item_id && (
+            <div className="plan-actions-list__header">
+              <div className="list-item-main">
+                <Link to={actionPath(action.id)} className="plan-actions-list__title">
+                  <strong>{action.title}</strong>
+                </Link>
                 <p className="list-item-sub muted">
-                  Gate: {gateTitleById(roadmapItems, action.roadmap_item_id)}
+                  {formatProjectContext(projects, action.project_id)}
                 </p>
-              )}
-              {action.description && (
-                <p className="list-item-desc">{action.description}</p>
-              )}
-            </div>
-            <div className="list-item-meta action-controls">
-              <StatusBadge kind="action" status={action.status} />
-              <PriorityBadge priority={action.priority} />
-              <Link to={actionPath(action.id)} className="btn btn-secondary btn-sm">
-                Öffnen
-              </Link>
+                {action.roadmap_item_id && (
+                  <p className="list-item-sub muted">
+                    Gate: {gateTitleById(roadmapItems, action.roadmap_item_id)}
+                  </p>
+                )}
+                {action.description && (
+                  <p className="list-item-desc">{action.description}</p>
+                )}
+              </div>
+              <div className="list-item-meta action-controls">
+                <StatusBadge kind="action" status={action.status} />
+                <PriorityBadge priority={action.priority} />
+                <Link to={actionPath(action.id)} className="btn btn-secondary btn-sm">
+                  Öffnen
+                </Link>
+              </div>
             </div>
+            <ActionTaskPanel
+              actionId={action.id}
+              roadmapItems={roadmapItems}
+              canManage={canManage}
+              expanded={expandedActions.has(action.id)}
+              onToggle={() => toggleActionTasks(action.id)}
+            />
           </li>
         ))}
       </ul>
diff --git a/frontend/src/components/TaskForm.jsx b/frontend/src/components/TaskForm.jsx
new file mode 100644
index 0000000..feb7eb7
--- /dev/null
+++ b/frontend/src/components/TaskForm.jsx
@@ -0,0 +1,179 @@
+import { TASK_STATUSES, TASK_STATUS_LABELS } from '../constants/status.js'
+import { gateTitleById } from './GateSelect.jsx'
+import { MAX_TASK_UI_DEPTH } from '../utils/taskTree.js'
+
+export function TaskForm({
+  initial = {},
+  parentTaskId = null,
+  parentLabel = null,
+  roadmapItems = [],
+  onSubmit,
+  onCancel,
+  busy = false,
+  submitLabel = 'Speichern',
+}) {
+  async function handleSubmit(e) {
+    e.preventDefault()
+    const form = e.target
+    await onSubmit({
+      title: form.title.value.trim(),
+      description: form.description.value,
+      status: form.status?.value || initial.status || 'open',
+      roadmap_item_id: form.roadmap_item_id?.value || undefined,
+      parent_task_id: parentTaskId || undefined,
+    })
+  }
+
+  return (
+    <form className="form workspace-form" onSubmit={handleSubmit}>
+      {parentLabel && (
+        <p className="muted task-form__parent-hint">Unteraufgabe von: {parentLabel}</p>
+      )}
+      <label>
+        Titel
+        <input
+          name="title"
+          defaultValue={initial.title || ''}
+          required
+          maxLength={255}
+          autoFocus
+        />
+      </label>
+      <label>
+        Beschreibung
+        <textarea name="description" rows={3} defaultValue={initial.description || ''} />
+      </label>
+      {roadmapItems.length > 0 && (
+        <label>
+          Gate (optional)
+          <select name="roadmap_item_id" defaultValue={initial.roadmap_item_id || ''}>
+            <option value="">— keins —</option>
+            {roadmapItems.map((item) => (
+              <option key={item.id} value={item.id}>
+                {item.title}
+              </option>
+            ))}
+          </select>
+        </label>
+      )}
+      {initial.id && (
+        <label>
+          Status
+          <select name="status" defaultValue={initial.status || 'open'}>
+            {TASK_STATUSES.map((status) => (
+              <option key={status} value={status}>
+                {TASK_STATUS_LABELS[status]}
+              </option>
+            ))}
+          </select>
+        </label>
+      )}
+      <div className="form-actions">
+        <button type="submit" className="btn btn-primary" disabled={busy}>
+          {busy ? 'Speichern …' : submitLabel}
+        </button>
+        {onCancel && (
+          <button type="button" className="btn btn-secondary" onClick={onCancel} disabled={busy}>
+            Abbrechen
+          </button>
+        )}
+      </div>
+    </form>
+  )
+}
+
+export function TaskTreeNodes({
+  tasksByParent,
+  parentId = '',
+  depth = 1,
+  roadmapItems,
+  canManage,
+  busy,
+  onEdit,
+  onAddSubtask,
+  onStatusChange,
+  onDelete,
+}) {
+  const nodes = tasksByParent.get(parentId || '') || []
+  if (!nodes.length) return null
+
+  return (
+    <ul className={`task-tree task-tree--depth-${depth}`}>
+      {nodes.map((task) => (
+        <li key={task.id} className="task-tree__item">
+          <div className="task-tree__row">
+            <div className="task-tree__main">
+              <strong>{task.title}</strong>
+              {task.roadmap_item_id && (
+                <span className="muted task-tree__gate">
+                  Gate: {gateTitleById(roadmapItems, task.roadmap_item_id)}
+                </span>
+              )}
+            </div>
+            <div className="task-tree__actions action-controls">
+              {canManage ? (
+                <>
+                  <select
+                    className="inline-select"
+                    value={task.status}
+                    disabled={busy}
+                    onChange={(e) => onStatusChange(task.id, e.target.value)}
+                    aria-label="Task-Status"
+                  >
+                    {TASK_STATUSES.map((status) => (
+                      <option key={status} value={status}>
+                        {TASK_STATUS_LABELS[status]}
+                      </option>
+                    ))}
+                  </select>
+                  {depth < MAX_TASK_UI_DEPTH && (
+                    <button
+                      type="button"
+                      className="btn btn-secondary btn-sm"
+                      disabled={busy}
+                      onClick={() => onAddSubtask(task)}
+                    >
+                      + Unteraufgabe
+                    </button>
+                  )}
+                  <button
+                    type="button"
+                    className="btn btn-secondary btn-sm"
+                    disabled={busy}
+                    onClick={() => onEdit(task)}
+                  >
+                    Bearbeiten
+                  </button>
+                  <button
+                    type="button"
+                    className="btn btn-secondary btn-sm"
+                    disabled={busy}
+                    onClick={() => onDelete(task.id)}
+                  >
+                    Entfernen
+                  </button>
+                </>
+              ) : (
+                <span>{TASK_STATUS_LABELS[task.status] || task.status}</span>
+              )}
+            </div>
+          </div>
+          {depth < MAX_TASK_UI_DEPTH && (
+            <TaskTreeNodes
+              tasksByParent={tasksByParent}
+              parentId={task.id}
+              depth={depth + 1}
+              roadmapItems={roadmapItems}
+              canManage={canManage}
+              busy={busy}
+              onEdit={onEdit}
+              onAddSubtask={onAddSubtask}
+              onStatusChange={onStatusChange}
+              onDelete={onDelete}
+            />
+          )}
+        </li>
+      ))}
+    </ul>
+  )
+}
diff --git a/frontend/src/styles/program-chrome.css b/frontend/src/styles/program-chrome.css
index ade3176..529e71d 100644
--- a/frontend/src/styles/program-chrome.css
+++ b/frontend/src/styles/program-chrome.css
@@ -430,3 +430,68 @@
 .plan-actions-section__scope-hint {
   margin: 0 0 12px;
 }
+
+.plan-actions-list__header {
+  display: flex;
+  flex-wrap: wrap;
+  justify-content: space-between;
+  gap: 12px;
+}
+
+.action-task-panel {
+  margin-top: 12px;
+  padding-top: 12px;
+  border-top: 1px solid var(--jk-border-subtle, #e5e7eb);
+}
+
+.action-task-panel__toggle {
+  background: none;
+  border: none;
+  padding: 0;
+  font: inherit;
+  color: var(--jk-primary, #2563eb);
+  cursor: pointer;
+}
+
+.action-task-panel__body {
+  margin-top: 10px;
+}
+
+.action-task-panel__add {
+  margin-top: 10px;
+}
+
+.task-tree {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+}
+
+.task-tree--depth-2,
+.task-tree--depth-3 {
+  margin-left: 16px;
+  padding-left: 12px;
+  border-left: 2px solid var(--jk-border-subtle, #e5e7eb);
+}
+
+.task-tree__item {
+  margin-bottom: 8px;
+}
+
+.task-tree__row {
+  display: flex;
+  flex-wrap: wrap;
+  justify-content: space-between;
+  gap: 8px;
+  align-items: flex-start;
+}
+
+.task-tree__gate {
+  display: block;
+  font-size: 13px;
+}
+
+.task-form__parent-hint {
+  margin: 0 0 12px;
+  font-size: 13px;
+}
diff --git a/frontend/src/utils/taskTree.js b/frontend/src/utils/taskTree.js
new file mode 100644
index 0000000..c8cc205
--- /dev/null
+++ b/frontend/src/utils/taskTree.js
@@ -0,0 +1,56 @@
+/** Task-Baum unter Action (AP1.5d) — UI max. 3 Ebenen. */
+
+export const MAX_TASK_UI_DEPTH = 3
+
+/**
+ * @param {Array<{ id: string, parent_task_id?: string | null, sort_order?: number, title?: string }>} tasks
+ * @returns {Map<string, Array<object>>}
+ */
+export function buildTasksByParent(tasks) {
+  const byParent = new Map()
+  for (const task of tasks) {
+    const parentKey = task.parent_task_id || ''
+    if (!byParent.has(parentKey)) {
+      byParent.set(parentKey, [])
+    }
+    byParent.get(parentKey).push(task)
+  }
+  for (const list of byParent.values()) {
+    list.sort(
+      (a, b) =>
+        (a.sort_order ?? 0) - (b.sort_order ?? 0) ||
+        (a.title || '').localeCompare(b.title || ''),
+    )
+  }
+  return byParent
+}
+
+/**
+ * @param {Map<string, Array<object>>} byParent
+ * @param {string | null | undefined} parentId
+ * @param {number} [depth]
+ * @returns {number}
+ */
+export function countOpenTasksInSubtree(byParent, parentId = '', depth = 1) {
+  const nodes = byParent.get(parentId || '') || []
+  let count = 0
+  for (const task of nodes) {
+    if (task.status !== 'done' && task.status !== 'discarded') {
+      count += 1
+    }
+    if (depth < MAX_TASK_UI_DEPTH) {
+      count += countOpenTasksInSubtree(byParent, task.id, depth + 1)
+    }
+  }
+  return count
+}
+
+/**
+ * @param {Array<object>} tasks
+ * @returns {number}
+ */
+export function countOpenTasks(tasks) {
+  if (!tasks?.length) return 0
+  const byParent = buildTasksByParent(tasks)
+  return countOpenTasksInSubtree(byParent)
+}
diff --git a/frontend/src/utils/taskTree.test.js b/frontend/src/utils/taskTree.test.js
new file mode 100644
index 0000000..f2990ea
--- /dev/null
+++ b/frontend/src/utils/taskTree.test.js
@@ -0,0 +1,23 @@
+import { describe, expect, it } from 'vitest'
+import { buildTasksByParent, countOpenTasks } from './taskTree.js'
+
+describe('taskTree', () => {
+  it('groups tasks by parent and sorts by sort_order', () => {
+    const byParent = buildTasksByParent([
+      { id: 'b', parent_task_id: 'a', sort_order: 2, title: 'B', status: 'open' },
+      { id: 'a', parent_task_id: null, sort_order: 1, title: 'A', status: 'open' },
+      { id: 'c', parent_task_id: 'a', sort_order: 1, title: 'C', status: 'done' },
+    ])
+    expect(byParent.get('').map((t) => t.id)).toEqual(['a'])
+    expect(byParent.get('a').map((t) => t.id)).toEqual(['c', 'b'])
+  })
+
+  it('counts open tasks in subtree', () => {
+    const tasks = [
+      { id: 'a', parent_task_id: null, status: 'open' },
+      { id: 'b', parent_task_id: 'a', status: 'done' },
+      { id: 'c', parent_task_id: 'a', status: 'open' },
+    ]
+    expect(countOpenTasks(tasks)).toBe(2)
+  })
+})