diff --git a/V3_MIGRATION_PLAN.md b/V3_MIGRATION_PLAN.md
index d2ef537..7829dcb 100644
--- a/V3_MIGRATION_PLAN.md
+++ b/V3_MIGRATION_PLAN.md
@@ -285,7 +285,7 @@ pytest tests/test_memory_models.py
 ```
 
 **Status**:
-- [ ] Step 6 complete
+- [x] Step 6 complete
 
 **Commit**: After tests pass, commit with:
 ```
diff --git a/alembic/versions/004_add_memory_tables.py b/alembic/versions/004_add_memory_tables.py
new file mode 100644
index 0000000..7a062cb
--- /dev/null
+++ b/alembic/versions/004_add_memory_tables.py
@@ -0,0 +1,144 @@
+"""Add memory tables and user encryption_key column.
+
+Memory tables:
+  memory_core        — per-user key/value preferences (encrypted)
+  memory_associative — semantic memory with pgvector embedding (encrypted)
+  memory_episodic    — session summaries (encrypted)
+  memory_proactive   — behavioral patterns (encrypted)
+
+Also adds encryption_key column to users table.
+
+Revision ID: 004
+Revises: 003
+Create Date: 2026-03-08
+"""
+
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "004"
+down_revision: Union[str, None] = "003"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # ── Enable pgvector extension (idempotent) ────────────────────────────────
+    op.execute("CREATE EXTENSION IF NOT EXISTS vector;")
+
+    # ── Add encryption_key to users ───────────────────────────────────────────
+    op.add_column(
+        "users",
+        sa.Column("encryption_key", sa.String(64), nullable=True),
+    )
+
+    # ── memory_core ───────────────────────────────────────────────────────────
+    op.create_table(
+        "memory_core",
+        sa.Column("id", sa.String(36), primary_key=True),
+        sa.Column(
+            "user_id",
+            sa.String(36),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+            index=True,
+        ),
+        sa.Column("key", sa.String(255), nullable=False),
+        sa.Column("value_encrypted", sa.Text, nullable=False),
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.func.now(),
+        ),
+    )
+    op.create_index("ix_memory_core_user_id", "memory_core", ["user_id"])
+
+    # ── memory_associative ────────────────────────────────────────────────────
+    # The embedding column uses pgvector's vector(1536) type.
+    op.create_table(
+        "memory_associative",
+        sa.Column("id", sa.String(36), primary_key=True),
+        sa.Column(
+            "user_id",
+            sa.String(36),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("content_encrypted", sa.Text, nullable=False),
+        sa.Column("entity_type", sa.String(100), nullable=True),
+        sa.Column("entity_id", sa.String(255), nullable=True),
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.func.now(),
+        ),
+    )
+    # Add the pgvector column separately (not supported by generic sa types)
+    op.execute(
+        "ALTER TABLE memory_associative ADD COLUMN embedding vector(1536);"
+    )
+    op.create_index("ix_memory_associative_user_id", "memory_associative", ["user_id"])
+    # IVFFlat index for approximate nearest-neighbour search
+    op.execute(
+        "CREATE INDEX ix_memory_associative_embedding "
+        "ON memory_associative USING ivfflat (embedding vector_cosine_ops) WITH (lists = 100);"
+    )
+
+    # ── memory_episodic ───────────────────────────────────────────────────────
+    op.create_table(
+        "memory_episodic",
+        sa.Column("id", sa.String(36), primary_key=True),
+        sa.Column(
+            "user_id",
+            sa.String(36),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("summary_encrypted", sa.Text, nullable=False),
+        sa.Column("session_id", sa.String(255), nullable=False),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.func.now(),
+        ),
+    )
+    op.create_index("ix_memory_episodic_user_id", "memory_episodic", ["user_id"])
+    op.create_index("ix_memory_episodic_session_id", "memory_episodic", ["session_id"])
+
+    # ── memory_proactive ──────────────────────────────────────────────────────
+    op.create_table(
+        "memory_proactive",
+        sa.Column("id", sa.String(36), primary_key=True),
+        sa.Column(
+            "user_id",
+            sa.String(36),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("pattern_encrypted", sa.Text, nullable=False),
+        sa.Column("confidence", sa.Float, nullable=False, server_default="0.5"),
+        sa.Column("source", sa.String(50), nullable=False, server_default="inferred"),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.func.now(),
+        ),
+    )
+    op.create_index("ix_memory_proactive_user_id", "memory_proactive", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_table("memory_proactive")
+    op.drop_table("memory_episodic")
+    op.drop_index("ix_memory_associative_embedding", "memory_associative")
+    op.drop_table("memory_associative")
+    op.drop_table("memory_core")
+    op.drop_column("users", "encryption_key")
diff --git a/app/api/routes/auth.py b/app/api/routes/auth.py
index 0fb3046..b32925e 100644
--- a/app/api/routes/auth.py
+++ b/app/api/routes/auth.py
@@ -13,6 +13,7 @@ import uuid
 from datetime import datetime, timedelta, timezone
 
 import bcrypt
+from cryptography.fernet import Fernet
 from fastapi import APIRouter, Depends, HTTPException, status
 from jose import jwt
 from pydantic import BaseModel
@@ -94,6 +95,7 @@ async def register(
         email=body.email,
         password_hash=_hash_password(body.password),
         tier="free",
+        encryption_key=Fernet.generate_key().decode(),
     )
     db.add(user)
     await db.flush()  # get user.id without committing
diff --git a/app/models.py b/app/models.py
index ed59042..e0e5f7f 100644
--- a/app/models.py
+++ b/app/models.py
@@ -14,6 +14,10 @@ Table inventory:
   plugin_installations — per-user install records
   plugin_reviews      — admin review decisions
   revenue_events      — Stripe Connect 70/30 split ledger
+  memory_core         — per-user persistent key/value preferences (encrypted)
+  memory_associative  — per-user semantic memory with embeddings (encrypted)
+  memory_episodic     — per-user session summaries (encrypted)
+  memory_proactive    — per-user behavioral patterns (encrypted)
 """
 
 from __future__ import annotations
@@ -74,6 +78,9 @@ class User(Base):
     password_hash: Mapped[str] = mapped_column(String(255), nullable=False)
     tier: Mapped[str] = mapped_column(TierEnum, nullable=False, default="free")
     stripe_customer_id: Mapped[str | None] = mapped_column(String(255), nullable=True)
+    # Per-user Fernet key (base64-urlsafe, 44 chars). Generated on registration.
+    # Used to encrypt/decrypt all memory rows for this user.
+    encryption_key: Mapped[str | None] = mapped_column(String(64), nullable=True)
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False, server_default=func.now()
     )
@@ -375,3 +382,93 @@ class AgentRunLog(Base):
         foreign_keys="AgentRunLog.agent_id",
         overlaps="run_logs,local_agent",
     )
+
+
+# ── Memory models ─────────────────────────────────────────────────────────────
+
+
+class MemoryCore(Base):
+    """Per-user persistent key/value preferences, encrypted at rest.
+
+    Examples: preferred_language, timezone, work_style.
+    Decrypted in-memory only using User.encryption_key.
+    """
+
+    __tablename__ = "memory_core"
+
+    id: Mapped[str] = mapped_column(Uuid(as_uuid=False), primary_key=True, default=_uuid)
+    user_id: Mapped[str] = mapped_column(
+        Uuid(as_uuid=False), ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False, index=True,
+    )
+    key: Mapped[str] = mapped_column(String(255), nullable=False)
+    value_encrypted: Mapped[str] = mapped_column(Text, nullable=False)
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, server_default=func.now(), onupdate=func.now()
+    )
+
+
+class MemoryAssociative(Base):
+    """Per-user semantic memory: encrypted content + pgvector embedding for similarity search.
+
+    Production: ``embedding`` column is ``vector(1536)`` via pgvector.
+    Tests (SQLite): stored as JSON list.
+    """
+
+    __tablename__ = "memory_associative"
+
+    id: Mapped[str] = mapped_column(Uuid(as_uuid=False), primary_key=True, default=_uuid)
+    user_id: Mapped[str] = mapped_column(
+        Uuid(as_uuid=False), ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False, index=True,
+    )
+    content_encrypted: Mapped[str] = mapped_column(Text, nullable=False)
+    # JSON-encoded float list in SQLite tests; vector(1536) in Postgres via migration.
+    embedding: Mapped[list | None] = mapped_column(JSON, nullable=True)
+    entity_type: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    entity_id: Mapped[str | None] = mapped_column(String(255), nullable=True)
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, server_default=func.now(), onupdate=func.now()
+    )
+
+
+class MemoryEpisodic(Base):
+    """Per-user session summaries, encrypted at rest.
+
+    One row per session interaction; used to recall recent conversations.
+    """
+
+    __tablename__ = "memory_episodic"
+
+    id: Mapped[str] = mapped_column(Uuid(as_uuid=False), primary_key=True, default=_uuid)
+    user_id: Mapped[str] = mapped_column(
+        Uuid(as_uuid=False), ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False, index=True,
+    )
+    summary_encrypted: Mapped[str] = mapped_column(Text, nullable=False)
+    session_id: Mapped[str] = mapped_column(String(255), nullable=False, index=True)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, server_default=func.now()
+    )
+
+
+class MemoryProactive(Base):
+    """Per-user inferred behavioral patterns, encrypted at rest.
+
+    Confidence in [0.0, 1.0]; only patterns above threshold are injected.
+    Source: 'inferred' (from episodes) or 'explicit' (user-stated).
+    """
+
+    __tablename__ = "memory_proactive"
+
+    id: Mapped[str] = mapped_column(Uuid(as_uuid=False), primary_key=True, default=_uuid)
+    user_id: Mapped[str] = mapped_column(
+        Uuid(as_uuid=False), ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False, index=True,
+    )
+    pattern_encrypted: Mapped[str] = mapped_column(Text, nullable=False)
+    confidence: Mapped[float] = mapped_column(Float, nullable=False, default=0.5)
+    source: Mapped[str] = mapped_column(String(50), nullable=False, default="inferred")
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, server_default=func.now()
+    )
diff --git a/tests/test_memory_models.py b/tests/test_memory_models.py
new file mode 100644
index 0000000..bea03d7
--- /dev/null
+++ b/tests/test_memory_models.py
@@ -0,0 +1,205 @@
+"""Tests for Step 6 — memory ORM models and User.encryption_key.
+
+Uses the SQLite in-memory test DB (from conftest). The pgvector embedding
+column is stored as JSON in tests (SQLite-compatible).
+"""
+
+from __future__ import annotations
+
+import uuid
+from datetime import datetime, timezone
+
+import pytest
+import pytest_asyncio
+from cryptography.fernet import Fernet
+from sqlalchemy import select
+
+from app.models import MemoryAssociative, MemoryCore, MemoryEpisodic, MemoryProactive, User
+from tests.conftest import TEST_USER_IDS
+
+
+USER_ID = TEST_USER_IDS["power"]
+
+
+# ── helpers ───────────────────────────────────────────────────────────────────
+
+def _fernet_key() -> str:
+    return Fernet.generate_key().decode()
+
+
+def _encrypt(key: str, plaintext: str) -> str:
+    return Fernet(key.encode()).encrypt(plaintext.encode()).decode()
+
+
+def _decrypt(key: str, ciphertext: str) -> str:
+    return Fernet(key.encode()).decrypt(ciphertext.encode()).decode()
+
+
+# ── User.encryption_key ───────────────────────────────────────────────────────
+
+@pytest.mark.asyncio
+async def test_user_encryption_key_column_exists(db_session):
+    """User model has encryption_key column and it can be set."""
+    result = await db_session.execute(select(User).where(User.id == USER_ID))
+    user = result.scalar_one()
+    # Column exists (may be None for seeded users)
+    assert hasattr(user, "encryption_key")
+
+
+@pytest.mark.asyncio
+async def test_user_encryption_key_can_be_set(db_session):
+    key = _fernet_key()
+    result = await db_session.execute(select(User).where(User.id == USER_ID))
+    user = result.scalar_one()
+    user.encryption_key = key
+    await db_session.commit()
+
+    result2 = await db_session.execute(select(User).where(User.id == USER_ID))
+    user2 = result2.scalar_one()
+    assert user2.encryption_key == key
+
+
+# ── MemoryCore ────────────────────────────────────────────────────────────────
+
+@pytest.mark.asyncio
+async def test_memory_core_create_and_read(db_session):
+    key = _fernet_key()
+    encrypted_val = _encrypt(key, "UTC")
+
+    row = MemoryCore(
+        id=str(uuid.uuid4()),
+        user_id=USER_ID,
+        key="timezone",
+        value_encrypted=encrypted_val,
+    )
+    db_session.add(row)
+    await db_session.commit()
+
+    result = await db_session.execute(
+        select(MemoryCore).where(MemoryCore.user_id == USER_ID)
+    )
+    fetched = result.scalar_one()
+    assert fetched.key == "timezone"
+    assert _decrypt(key, fetched.value_encrypted) == "UTC"
+
+
+@pytest.mark.asyncio
+async def test_memory_core_cascade_delete(db_session):
+    """Deleting a user cascades to memory_core."""
+    row = MemoryCore(
+        id=str(uuid.uuid4()),
+        user_id=USER_ID,
+        key="lang",
+        value_encrypted="enc",
+    )
+    db_session.add(row)
+    await db_session.commit()
+
+    user = (await db_session.execute(select(User).where(User.id == USER_ID))).scalar_one()
+    await db_session.delete(user)
+    await db_session.commit()
+
+    remaining = (
+        await db_session.execute(select(MemoryCore).where(MemoryCore.user_id == USER_ID))
+    ).scalars().all()
+    assert remaining == []
+
+
+# ── MemoryAssociative ─────────────────────────────────────────────────────────
+
+@pytest.mark.asyncio
+async def test_memory_associative_create_and_read(db_session):
+    key = _fernet_key()
+    content = _encrypt(key, "User prefers morning meetings")
+    embedding = [0.1] * 1536  # fake embedding
+
+    row = MemoryAssociative(
+        id=str(uuid.uuid4()),
+        user_id=USER_ID,
+        content_encrypted=content,
+        embedding=embedding,
+        entity_type="preference",
+        entity_id=None,
+    )
+    db_session.add(row)
+    await db_session.commit()
+
+    result = await db_session.execute(
+        select(MemoryAssociative).where(MemoryAssociative.user_id == USER_ID)
+    )
+    fetched = result.scalar_one()
+    assert fetched.entity_type == "preference"
+    assert _decrypt(key, fetched.content_encrypted) == "User prefers morning meetings"
+    assert len(fetched.embedding) == 1536
+
+
+# ── MemoryEpisodic ────────────────────────────────────────────────────────────
+
+@pytest.mark.asyncio
+async def test_memory_episodic_create_and_read(db_session):
+    key = _fernet_key()
+    session_id = str(uuid.uuid4())
+    summary = _encrypt(key, "User asked about Q1 tasks")
+
+    row = MemoryEpisodic(
+        id=str(uuid.uuid4()),
+        user_id=USER_ID,
+        summary_encrypted=summary,
+        session_id=session_id,
+    )
+    db_session.add(row)
+    await db_session.commit()
+
+    result = await db_session.execute(
+        select(MemoryEpisodic).where(MemoryEpisodic.session_id == session_id)
+    )
+    fetched = result.scalar_one()
+    assert _decrypt(key, fetched.summary_encrypted) == "User asked about Q1 tasks"
+    assert isinstance(fetched.created_at, datetime)
+
+
+# ── MemoryProactive ───────────────────────────────────────────────────────────
+
+@pytest.mark.asyncio
+async def test_memory_proactive_create_and_read(db_session):
+    key = _fernet_key()
+    pattern = _encrypt(key, "User always assigns tasks to self")
+
+    row = MemoryProactive(
+        id=str(uuid.uuid4()),
+        user_id=USER_ID,
+        pattern_encrypted=pattern,
+        confidence=0.85,
+        source="inferred",
+    )
+    db_session.add(row)
+    await db_session.commit()
+
+    result = await db_session.execute(
+        select(MemoryProactive).where(MemoryProactive.user_id == USER_ID)
+    )
+    fetched = result.scalar_one()
+    assert fetched.confidence == pytest.approx(0.85)
+    assert fetched.source == "inferred"
+    assert _decrypt(key, fetched.pattern_encrypted) == "User always assigns tasks to self"
+
+
+# ── Auth registration generates encryption_key ───────────────────────────────
+
+def test_register_sets_encryption_key(client):
+    """POST /api/v1/auth/register creates a user with a valid Fernet key."""
+    resp = client.post(
+        "/api/v1/auth/register",
+        json={"email": "newuser@test.com", "password": "testpassword123"},
+    )
+    assert resp.status_code == 201
+
+    # Fetch the newly created user via the access token
+    token = resp.json()["access_token"]
+    me_resp = client.get(
+        "/api/v1/auth/me",
+        headers={"Authorization": f"Bearer {token}"},
+    )
+    assert me_resp.status_code == 200
+    # We can't see encryption_key in the API response (not in UserProfile),
+    # but we verify registration didn't crash — key generation is implicit.