diff --git a/api/main.py b/api/main.py
index ad5afea..261ddfc 100644
--- a/api/main.py
+++ b/api/main.py
@@ -30,6 +30,7 @@
 from api.gdpr import router as gdpr_router
 from api.memory_state import router as memory_state_router
 from api.reliability import router as reliability_router
+from api.outcomes import router as outcomes_router
 from api.metrics import record_http_request, record_query, render_metrics
 from api.decisions import router as decisions_router
 from api.deps import RolesDep, memory, set_memory_service
@@ -111,6 +112,7 @@ async def lifespan(app: FastAPI) -> AsyncIterator[None]:
 app.include_router(evidence_router)
 app.include_router(memory_state_router)
 app.include_router(reliability_router)
+app.include_router(outcomes_router)
 
 
 @app.middleware("http")
diff --git a/api/outcomes.py b/api/outcomes.py
new file mode 100644
index 0000000..b5916b1
--- /dev/null
+++ b/api/outcomes.py
@@ -0,0 +1,53 @@
+"""POST /outcomes/record — append action ledger entry."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from fastapi import APIRouter
+from pydantic import BaseModel, Field
+
+from api.deps import RolesDep
+from outcomes.ledger import ActionLedgerEntry, record_outcome, update_usefulness
+
+router = APIRouter(prefix="/outcomes", tags=["outcomes"])
+
+
+class RecordOutcomeRequest(BaseModel):
+    workspace_id: str
+    agent_id: str
+    task: str
+    memory_ids: list[str] = Field(default_factory=list)
+    reliability_decision: str | None = None
+    action: dict[str, Any] = Field(default_factory=dict)
+    outcome: str = "unknown"
+    metrics: dict[str, Any] = Field(default_factory=dict)
+    prior_usefulness: float = Field(default=0.5, ge=0.0, le=1.0)
+    trace_id: str | None = None
+
+
+class RecordOutcomeResponse(BaseModel):
+    id: str
+    usefulness_score: float
+
+
+@router.post("/record", response_model=RecordOutcomeResponse)
+def post_record_outcome(body: RecordOutcomeRequest, _roles: RolesDep) -> RecordOutcomeResponse:
+    entry = ActionLedgerEntry(
+        workspace_id=body.workspace_id,
+        agent_id=body.agent_id,
+        task=body.task,
+        memory_ids=body.memory_ids,
+        reliability_decision=body.reliability_decision,
+        action=body.action,
+        outcome=body.outcome,  # type: ignore[arg-type]
+        metrics=body.metrics,
+        trace_id=body.trace_id,
+    )
+    record_outcome(entry)
+    success = body.outcome == "success"
+    usefulness = update_usefulness(
+        prior_usefulness=body.prior_usefulness,
+        success=success,
+    )
+    return RecordOutcomeResponse(id=entry.id, usefulness_score=usefulness)
diff --git a/outcomes/__init__.py b/outcomes/__init__.py
new file mode 100644
index 0000000..f2030cd
--- /dev/null
+++ b/outcomes/__init__.py
@@ -0,0 +1,15 @@
+"""Outcome-driven memory updating package."""
+
+from outcomes.ledger import (
+    ActionLedgerEntry,
+    OutcomeRecord,
+    record_outcome,
+    update_usefulness,
+)
+
+__all__ = [
+    "ActionLedgerEntry",
+    "OutcomeRecord",
+    "record_outcome",
+    "update_usefulness",
+]
diff --git a/outcomes/ledger.py b/outcomes/ledger.py
new file mode 100644
index 0000000..2189029
--- /dev/null
+++ b/outcomes/ledger.py
@@ -0,0 +1,75 @@
+"""Outcome ledger and usefulness updates (V2 Enhancement 5)."""
+
+from __future__ import annotations
+
+import uuid
+from datetime import UTC, datetime
+from typing import Any, Literal
+
+from pydantic import BaseModel, Field
+
+OutcomeResult = Literal["success", "failure", "partial", "unknown"]
+
+
+def _uuid4() -> str:
+    return str(uuid.uuid4())
+
+
+def _utcnow() -> datetime:
+    return datetime.now(UTC)
+
+
+class ActionLedgerEntry(BaseModel):
+    """Append-oriented audit of agent action + memory used."""
+
+    id: str = Field(default_factory=_uuid4)
+    workspace_id: str
+    agent_id: str
+    task: str
+    memory_ids: list[str] = Field(default_factory=list)
+    reliability_decision: str | None = None
+    action: dict[str, Any] = Field(default_factory=dict)
+    outcome: OutcomeResult = "unknown"
+    metrics: dict[str, Any] = Field(default_factory=dict)
+    trace_id: str | None = None
+    created_at: datetime = Field(default_factory=_utcnow)
+
+
+class OutcomeRecord(BaseModel):
+    """Outcome linked to a decision or procedure."""
+
+    id: str = Field(default_factory=_uuid4)
+    workspace_id: str
+    action_id: str | None = None
+    procedure_id: str | None = None
+    decision_id: str | None = None
+    result: OutcomeResult
+    success: bool
+    metrics: dict[str, Any] = Field(default_factory=dict)
+    observed_at: datetime = Field(default_factory=_utcnow)
+    evidence_ids: list[str] = Field(default_factory=list)
+
+
+def update_usefulness(
+    *,
+    prior_usefulness: float,
+    success: bool,
+    learning_rate: float = 0.1,
+) -> float:
+    """Update usefulness score without erasing history (bounded EMA)."""
+    target = 1.0 if success else 0.0
+    value = prior_usefulness + learning_rate * (target - prior_usefulness)
+    return max(0.0, min(1.0, round(value, 4)))
+
+
+_LEDGER: list[ActionLedgerEntry] = []
+
+
+def record_outcome(entry: ActionLedgerEntry) -> ActionLedgerEntry:
+    """Append to in-memory ledger (Neo4j writer can replace later)."""
+    _LEDGER.append(entry)
+    return entry
+
+
+def ledger_for_workspace(workspace_id: str) -> list[ActionLedgerEntry]:
+    return [e for e in _LEDGER if e.workspace_id == workspace_id]
diff --git a/tests/outcomes/test_ledger.py b/tests/outcomes/test_ledger.py
new file mode 100644
index 0000000..49bf4a3
--- /dev/null
+++ b/tests/outcomes/test_ledger.py
@@ -0,0 +1,9 @@
+from outcomes.ledger import update_usefulness
+
+
+def test_usefulness_rises_on_success() -> None:
+    assert update_usefulness(prior_usefulness=0.5, success=True) > 0.5
+
+
+def test_usefulness_falls_on_failure() -> None:
+    assert update_usefulness(prior_usefulness=0.5, success=False) < 0.5