diff --git a/backend/routers/catalogs.py b/backend/routers/catalogs.py
index 50d09cf..d4e7a76 100644
--- a/backend/routers/catalogs.py
+++ b/backend/routers/catalogs.py
@@ -721,3 +721,254 @@ def delete_target_group(target_group_id: int, session=Depends(require_auth)):
         conn.commit()
 
     return {"ok": True}
+
+
+# ════════════════════════════════════════════════════════════════════════
+# TRAINING STYLE → TARGET GROUPS (M:N Assignments)
+# ════════════════════════════════════════════════════════════════════════
+
+@router.get("/training-style-target-groups")
+def list_training_style_target_groups(
+    training_style_id: Optional[int] = Query(default=None),
+    target_group_id: Optional[int] = Query(default=None),
+    is_primary: Optional[bool] = Query(default=None),
+    session=Depends(require_auth)
+):
+    """List M:N assignments between training styles and target groups.
+
+    Returns enriched data with training_style_name, target_group_name,
+    focus_area_name for easy display in Matrix UI.
+    """
+    with get_db() as conn:
+        cur = get_cursor(conn)
+
+        query = """
+            SELECT
+                tstg.id,
+                tstg.training_style_id,
+                tstg.target_group_id,
+                tstg.is_primary,
+                tstg.created_at,
+                ts.name as training_style_name,
+                ts.focus_area_id,
+                fa.name as focus_area_name,
+                tg.name as target_group_name,
+                tg.min_age,
+                tg.max_age
+            FROM training_style_target_groups tstg
+            LEFT JOIN training_styles ts ON tstg.training_style_id = ts.id
+            LEFT JOIN focus_areas fa ON ts.focus_area_id = fa.id
+            LEFT JOIN target_groups tg ON tstg.target_group_id = tg.id
+        """
+        params = []
+        where = []
+
+        if training_style_id is not None:
+            where.append("tstg.training_style_id = %s")
+            params.append(training_style_id)
+
+        if target_group_id is not None:
+            where.append("tstg.target_group_id = %s")
+            params.append(target_group_id)
+
+        if is_primary is not None:
+            where.append("tstg.is_primary = %s")
+            params.append(is_primary)
+
+        if where:
+            query += " WHERE " + " AND ".join(where)
+
+        query += " ORDER BY fa.sort_order, ts.sort_order, tg.sort_order"
+
+        cur.execute(query, params)
+        rows = cur.fetchall()
+        return [r2d(r) for r in rows]
+
+
+@router.post("/training-style-target-groups")
+def create_training_style_target_group(data: dict, session=Depends(require_auth)):
+    """Assign target group to training style (admin only).
+
+    Uses UPSERT logic - if assignment exists, updates is_primary flag.
+    """
+    role = session.get('role')
+    if role not in ['admin', 'superadmin']:
+        raise HTTPException(403, "Nur Admins dürfen Zuordnungen erstellen")
+
+    training_style_id = data.get('training_style_id')
+    target_group_id = data.get('target_group_id')
+
+    if not training_style_id or not target_group_id:
+        raise HTTPException(400, "training_style_id und target_group_id sind Pflichtfelder")
+
+    with get_db() as conn:
+        cur = get_cursor(conn)
+
+        # Upsert logic
+        cur.execute("""
+            INSERT INTO training_style_target_groups
+                (training_style_id, target_group_id, is_primary)
+            VALUES (%s, %s, %s)
+            ON CONFLICT (training_style_id, target_group_id)
+            DO UPDATE SET is_primary = EXCLUDED.is_primary
+            RETURNING id
+        """, (
+            training_style_id,
+            target_group_id,
+            data.get('is_primary', False)
+        ))
+
+        assignment_id = cur.fetchone()['id']
+        conn.commit()
+
+        # Return enriched record
+        cur.execute("""
+            SELECT
+                tstg.id,
+                tstg.training_style_id,
+                tstg.target_group_id,
+                tstg.is_primary,
+                tstg.created_at,
+                ts.name as training_style_name,
+                ts.focus_area_id,
+                fa.name as focus_area_name,
+                tg.name as target_group_name
+            FROM training_style_target_groups tstg
+            LEFT JOIN training_styles ts ON tstg.training_style_id = ts.id
+            LEFT JOIN focus_areas fa ON ts.focus_area_id = fa.id
+            LEFT JOIN target_groups tg ON tstg.target_group_id = tg.id
+            WHERE tstg.id = %s
+        """, (assignment_id,))
+
+        return r2d(cur.fetchone())
+
+
+@router.put("/training-style-target-groups/{assignment_id}")
+def update_training_style_target_group(
+    assignment_id: int,
+    data: dict,
+    session=Depends(require_auth)
+):
+    """Update M:N assignment (admin only).
+
+    Currently only supports updating is_primary flag.
+    """
+    role = session.get('role')
+    if role not in ['admin', 'superadmin']:
+        raise HTTPException(403, "Nur Admins dürfen Zuordnungen bearbeiten")
+
+    with get_db() as conn:
+        cur = get_cursor(conn)
+
+        cur.execute("""
+            UPDATE training_style_target_groups
+            SET is_primary = %s
+            WHERE id = %s
+        """, (
+            data.get('is_primary', False),
+            assignment_id
+        ))
+
+        conn.commit()
+
+        # Return enriched record
+        cur.execute("""
+            SELECT
+                tstg.id,
+                tstg.training_style_id,
+                tstg.target_group_id,
+                tstg.is_primary,
+                tstg.created_at,
+                ts.name as training_style_name,
+                ts.focus_area_id,
+                fa.name as focus_area_name,
+                tg.name as target_group_name
+            FROM training_style_target_groups tstg
+            LEFT JOIN training_styles ts ON tstg.training_style_id = ts.id
+            LEFT JOIN focus_areas fa ON ts.focus_area_id = fa.id
+            LEFT JOIN target_groups tg ON tstg.target_group_id = tg.id
+            WHERE tstg.id = %s
+        """, (assignment_id,))
+
+        return r2d(cur.fetchone())
+
+
+@router.delete("/training-style-target-groups/{assignment_id}")
+def delete_training_style_target_group(assignment_id: int, session=Depends(require_auth)):
+    """Remove M:N assignment (admin only)."""
+    role = session.get('role')
+    if role not in ['admin', 'superadmin']:
+        raise HTTPException(403, "Nur Admins dürfen Zuordnungen löschen")
+
+    with get_db() as conn:
+        cur = get_cursor(conn)
+        cur.execute("DELETE FROM training_style_target_groups WHERE id = %s", (assignment_id,))
+        conn.commit()
+
+    return {"ok": True}
+
+
+@router.get("/training-styles/hierarchy")
+def get_training_styles_hierarchy(
+    status: Optional[str] = Query(default='active'),
+    session=Depends(require_auth)
+):
+    """Get hierarchical structure: Focus Areas → Training Styles → Target Groups.
+
+    Returns nested structure for Tree-View rendering in Admin UI.
+    """
+    with get_db() as conn:
+        cur = get_cursor(conn)
+
+        # Get all focus areas
+        fa_query = "SELECT * FROM focus_areas"
+        fa_params = []
+
+        if status:
+            fa_query += " WHERE status = %s"
+            fa_params.append(status)
+
+        fa_query += " ORDER BY sort_order, name"
+
+        cur.execute(fa_query, fa_params)
+        focus_areas = [r2d(r) for r in cur.fetchall()]
+
+        # For each focus area, get training styles with their target groups
+        for fa in focus_areas:
+            ts_query = """
+                SELECT * FROM training_styles
+                WHERE focus_area_id = %s
+            """
+            ts_params = [fa['id']]
+
+            if status:
+                ts_query += " AND status = %s"
+                ts_params.append(status)
+
+            ts_query += " ORDER BY sort_order, name"
+
+            cur.execute(ts_query, ts_params)
+            training_styles = [r2d(r) for r in cur.fetchall()]
+
+            # For each training style, get assigned target groups
+            for ts in training_styles:
+                cur.execute("""
+                    SELECT
+                        tg.id,
+                        tg.name,
+                        tg.description,
+                        tg.min_age,
+                        tg.max_age,
+                        tstg.is_primary,
+                        tstg.id as assignment_id
+                    FROM training_style_target_groups tstg
+                    LEFT JOIN target_groups tg ON tstg.target_group_id = tg.id
+                    WHERE tstg.training_style_id = %s
+                    ORDER BY tg.sort_order, tg.name
+                """, (ts['id'],))
+
+                ts['target_groups'] = [r2d(r) for r in cur.fetchall()]
+
+            fa['training_styles'] = training_styles
+
+        return focus_areas
diff --git a/backend/version.py b/backend/version.py
index ecdb529..3b62e38 100644
--- a/backend/version.py
+++ b/backend/version.py
@@ -1,6 +1,6 @@
 # Shinkan Jinkendo Version Information
 
-APP_VERSION = "0.3.3"
+APP_VERSION = "0.3.4"
 BUILD_DATE = "2026-04-23"
 DB_SCHEMA_VERSION = "20260423"
 
@@ -18,10 +18,25 @@ MODULE_VERSIONS = {
     "import_wiki": "0.1.0",
     "admin": "1.0.0",
     "membership": "1.0.0",
-    "catalogs": "1.2.0",  # Updated: Target Groups CRUD + Admin UI
+    "catalogs": "1.3.0",  # Updated: M:N Zielgruppen-Zuordnung (Migration 009)
 }
 
 CHANGELOG = [
+    {
+        "version": "0.3.4",
+        "date": "2026-04-23",
+        "changes": [
+            "BREAKING: Migration 009 - Zielgruppen M:N Refactoring",
+            "DB: target_groups.training_style_id entfernt (jetzt global unabhängig)",
+            "DB: Neue Junction-Tabelle training_style_target_groups (M:N)",
+            "API: 5 neue Endpoints für M:N Management (GET/POST/PUT/DELETE + hierarchy)",
+            "API: GET /training-style-target-groups mit Enrichment (focus_area_name, training_style_name)",
+            "API: GET /training-styles/hierarchy für Tree-View (verschachtelte Struktur)",
+            "API: POST /training-style-target-groups mit Upsert-Logik",
+            "Backward-Compatible: exercise_target_groups weiterhin unterstützt",
+            "Architecture: Eine Zielgruppe kann mehreren Stilen zugeordnet werden",
+        ]
+    },
     {
         "version": "0.3.3",
         "date": "2026-04-23",
diff --git a/frontend/src/version.js b/frontend/src/version.js
index dfec193..074ad2d 100644
--- a/frontend/src/version.js
+++ b/frontend/src/version.js
@@ -1,6 +1,6 @@
 // Shinkan Jinkendo Frontend Version
 
-export const APP_VERSION = "0.3.3"
+export const APP_VERSION = "0.3.4"
 export const BUILD_DATE = "2026-04-23"
 
 export const PAGE_VERSIONS = {