diff --git a/README.md b/README.md
index 6efcb67..4b803e8 100644
--- a/README.md
+++ b/README.md
@@ -85,10 +85,33 @@ Aegis/
 │       ├── __init__.py
 │       ├── main.py         # FastAPI application entry point
 │       ├── config.py       # Application settings
-│       └── database.py     # SQLAlchemy configuration
+│       ├── database.py     # SQLAlchemy configuration
+│       ├── models/         # SQLAlchemy models
+│       │   ├── user.py     # User authentication model
+│       │   ├── technique.py # MITRE ATT&CK techniques
+│       │   ├── test.py     # Security tests
+│       │   ├── evidence.py # Test evidence files
+│       │   ├── intel.py    # Threat intelligence items
+│       │   ├── audit.py    # Audit logging
+│       │   └── enums.py    # Shared enumerations
+│       └── services/       # Business logic services
+│           └── audit_service.py
 └── frontend/               # React frontend (coming soon)
 ```
 
+## Database Schema
+
+The platform uses the following data models:
+
+| Table | Description |
+|-------|-------------|
+| `users` | User accounts with role-based access |
+| `techniques` | MITRE ATT&CK techniques with coverage status |
+| `tests` | Security tests validating technique coverage |
+| `evidences` | File evidence attached to tests (stored in MinIO) |
+| `intel_items` | Threat intelligence items linked to techniques |
+| `audit_logs` | System-wide audit trail for all actions |
+
 ## Configuration
 
 The application can be configured via environment variables:
diff --git a/backend/alembic/env.py b/backend/alembic/env.py
index adabaab..80c2790 100644
--- a/backend/alembic/env.py
+++ b/backend/alembic/env.py
@@ -7,6 +7,7 @@ from alembic import context
 
 from app.database import Base
 from app.config import settings
+from app.models import *  # noqa: F401, F403 - Import all models for Alembic detection
 
 # this is the Alembic Config object, which provides
 # access to the values within the .ini file in use.
diff --git a/backend/alembic/versions/14c6f07b47cb_add_tests_table.py b/backend/alembic/versions/14c6f07b47cb_add_tests_table.py
new file mode 100644
index 0000000..0b43c17
--- /dev/null
+++ b/backend/alembic/versions/14c6f07b47cb_add_tests_table.py
@@ -0,0 +1,57 @@
+"""add_tests_table
+
+Revision ID: 14c6f07b47cb
+Revises: 476930a8d86e
+Create Date: 2026-02-06 11:01:01.822240
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = '14c6f07b47cb'
+down_revision: Union[str, Sequence[str], None] = '476930a8d86e'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # Create enum types
+    testresult_enum = postgresql.ENUM('detected', 'not_detected', 'partially_detected', name='testresult')
+    teststate_enum = postgresql.ENUM('draft', 'in_review', 'validated', 'rejected', name='teststate')
+    testresult_enum.create(op.get_bind(), checkfirst=True)
+    teststate_enum.create(op.get_bind(), checkfirst=True)
+    
+    # Create table
+    op.create_table('tests',
+    sa.Column('id', sa.UUID(), nullable=False),
+    sa.Column('technique_id', sa.UUID(), nullable=False),
+    sa.Column('name', sa.String(), nullable=False),
+    sa.Column('description', sa.Text(), nullable=True),
+    sa.Column('platform', sa.String(), nullable=True),
+    sa.Column('procedure_text', sa.Text(), nullable=True),
+    sa.Column('tool_used', sa.String(), nullable=True),
+    sa.Column('execution_date', sa.DateTime(), nullable=True),
+    sa.Column('created_by', sa.UUID(), nullable=True),
+    sa.Column('result', postgresql.ENUM('detected', 'not_detected', 'partially_detected', name='testresult', create_type=False), nullable=True),
+    sa.Column('state', postgresql.ENUM('draft', 'in_review', 'validated', 'rejected', name='teststate', create_type=False), nullable=True),
+    sa.Column('validated_by', sa.UUID(), nullable=True),
+    sa.Column('validated_at', sa.DateTime(), nullable=True),
+    sa.Column('created_at', sa.DateTime(), nullable=True),
+    sa.ForeignKeyConstraint(['created_by'], ['users.id'], ),
+    sa.ForeignKeyConstraint(['technique_id'], ['techniques.id'], ),
+    sa.ForeignKeyConstraint(['validated_by'], ['users.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    op.drop_table('tests')
+    # Drop enum types
+    postgresql.ENUM(name='testresult').drop(op.get_bind(), checkfirst=True)
+    postgresql.ENUM(name='teststate').drop(op.get_bind(), checkfirst=True)
diff --git a/backend/alembic/versions/4671fccfa705_add_users_table.py b/backend/alembic/versions/4671fccfa705_add_users_table.py
new file mode 100644
index 0000000..591ba1d
--- /dev/null
+++ b/backend/alembic/versions/4671fccfa705_add_users_table.py
@@ -0,0 +1,43 @@
+"""add_users_table
+
+Revision ID: 4671fccfa705
+Revises: f03e5712c21c
+Create Date: 2026-02-06 10:30:07.210676
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '4671fccfa705'
+down_revision: Union[str, Sequence[str], None] = 'f03e5712c21c'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('users',
+    sa.Column('id', sa.UUID(), nullable=False),
+    sa.Column('username', sa.String(), nullable=False),
+    sa.Column('email', sa.String(), nullable=True),
+    sa.Column('hashed_password', sa.String(), nullable=False),
+    sa.Column('role', sa.String(), nullable=False),
+    sa.Column('is_active', sa.Boolean(), nullable=True),
+    sa.Column('created_at', sa.DateTime(), nullable=True),
+    sa.Column('last_login', sa.DateTime(), nullable=True),
+    sa.PrimaryKeyConstraint('id'),
+    sa.UniqueConstraint('username')
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_table('users')
+    # ### end Alembic commands ###
diff --git a/backend/alembic/versions/476930a8d86e_add_techniques_table.py b/backend/alembic/versions/476930a8d86e_add_techniques_table.py
new file mode 100644
index 0000000..faf4553
--- /dev/null
+++ b/backend/alembic/versions/476930a8d86e_add_techniques_table.py
@@ -0,0 +1,54 @@
+"""add_techniques_table
+
+Revision ID: 476930a8d86e
+Revises: 4671fccfa705
+Create Date: 2026-02-06 10:37:17.777106
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = '476930a8d86e'
+down_revision: Union[str, Sequence[str], None] = '4671fccfa705'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # Create enum type explicitly
+    techniquestatus_enum = postgresql.ENUM(
+        'not_evaluated', 'in_progress', 'validated', 'partial', 'not_covered', 'review_required',
+        name='techniquestatus'
+    )
+    techniquestatus_enum.create(op.get_bind(), checkfirst=True)
+    
+    # Create table with create_type=False since we already created the enum
+    op.create_table('techniques',
+    sa.Column('id', sa.UUID(), nullable=False),
+    sa.Column('mitre_id', sa.String(), nullable=False),
+    sa.Column('name', sa.String(), nullable=False),
+    sa.Column('description', sa.Text(), nullable=True),
+    sa.Column('tactic', sa.String(), nullable=True),
+    sa.Column('platforms', postgresql.JSONB(astext_type=sa.Text()), nullable=True),
+    sa.Column('mitre_version', sa.String(), nullable=True),
+    sa.Column('mitre_last_modified', sa.DateTime(), nullable=True),
+    sa.Column('is_subtechnique', sa.Boolean(), nullable=True),
+    sa.Column('parent_mitre_id', sa.String(), nullable=True),
+    sa.Column('status_global', postgresql.ENUM('not_evaluated', 'in_progress', 'validated', 'partial', 'not_covered', 'review_required', name='techniquestatus', create_type=False), nullable=True),
+    sa.Column('review_required', sa.Boolean(), nullable=True),
+    sa.Column('last_review_date', sa.DateTime(), nullable=True),
+    sa.PrimaryKeyConstraint('id'),
+    sa.UniqueConstraint('mitre_id')
+    )
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    op.drop_table('techniques')
+    # Drop enum type after dropping table
+    postgresql.ENUM(name='techniquestatus').drop(op.get_bind(), checkfirst=True)
diff --git a/backend/alembic/versions/7cec59461d53_add_evidences_table.py b/backend/alembic/versions/7cec59461d53_add_evidences_table.py
new file mode 100644
index 0000000..a55c9bc
--- /dev/null
+++ b/backend/alembic/versions/7cec59461d53_add_evidences_table.py
@@ -0,0 +1,39 @@
+"""add_evidences_table
+
+Revision ID: 7cec59461d53
+Revises: 14c6f07b47cb
+Create Date: 2026-02-06 11:06:14.535381
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '7cec59461d53'
+down_revision: Union[str, Sequence[str], None] = '14c6f07b47cb'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    op.create_table('evidences',
+    sa.Column('id', sa.UUID(), nullable=False),
+    sa.Column('test_id', sa.UUID(), nullable=False),
+    sa.Column('file_name', sa.String(), nullable=False),
+    sa.Column('file_path', sa.String(), nullable=False),
+    sa.Column('sha256_hash', sa.String(), nullable=False),
+    sa.Column('uploaded_by', sa.UUID(), nullable=True),
+    sa.Column('uploaded_at', sa.DateTime(), nullable=True),
+    sa.ForeignKeyConstraint(['test_id'], ['tests.id'], ),
+    sa.ForeignKeyConstraint(['uploaded_by'], ['users.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    op.drop_table('evidences')
diff --git a/backend/alembic/versions/a1412d1ef337_add_audit_logs_table.py b/backend/alembic/versions/a1412d1ef337_add_audit_logs_table.py
new file mode 100644
index 0000000..ee71a0b
--- /dev/null
+++ b/backend/alembic/versions/a1412d1ef337_add_audit_logs_table.py
@@ -0,0 +1,38 @@
+"""add_audit_logs_table
+
+Revision ID: a1412d1ef337
+Revises: ef21f4a670ed
+Create Date: 2026-02-06 11:19:09.293785
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = 'a1412d1ef337'
+down_revision: Union[str, Sequence[str], None] = 'ef21f4a670ed'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    op.create_table('audit_logs',
+    sa.Column('id', sa.UUID(), nullable=False),
+    sa.Column('user_id', sa.UUID(), nullable=True),
+    sa.Column('action', sa.String(), nullable=False),
+    sa.Column('entity_type', sa.String(), nullable=True),
+    sa.Column('entity_id', sa.String(), nullable=True),
+    sa.Column('timestamp', sa.DateTime(), nullable=True),
+    sa.Column('details', postgresql.JSONB(astext_type=sa.Text()), nullable=True),
+    sa.ForeignKeyConstraint(['user_id'], ['users.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    op.drop_table('audit_logs')
diff --git a/backend/alembic/versions/ef21f4a670ed_add_intel_items_table.py b/backend/alembic/versions/ef21f4a670ed_add_intel_items_table.py
new file mode 100644
index 0000000..a2f4113
--- /dev/null
+++ b/backend/alembic/versions/ef21f4a670ed_add_intel_items_table.py
@@ -0,0 +1,38 @@
+"""add_intel_items_table
+
+Revision ID: ef21f4a670ed
+Revises: 7cec59461d53
+Create Date: 2026-02-06 11:10:30.452222
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'ef21f4a670ed'
+down_revision: Union[str, Sequence[str], None] = '7cec59461d53'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    op.create_table('intel_items',
+    sa.Column('id', sa.UUID(), nullable=False),
+    sa.Column('technique_id', sa.UUID(), nullable=True),
+    sa.Column('url', sa.String(), nullable=False),
+    sa.Column('title', sa.String(), nullable=True),
+    sa.Column('source', sa.String(), nullable=True),
+    sa.Column('detected_at', sa.DateTime(), nullable=True),
+    sa.Column('reviewed', sa.Boolean(), nullable=True),
+    sa.ForeignKeyConstraint(['technique_id'], ['techniques.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    op.drop_table('intel_items')
diff --git a/backend/app/models/__init__.py b/backend/app/models/__init__.py
new file mode 100644
index 0000000..cb09c57
--- /dev/null
+++ b/backend/app/models/__init__.py
@@ -0,0 +1,13 @@
+# Import all models here so Alembic can detect them
+from app.models.user import User
+from app.models.technique import Technique
+from app.models.test import Test
+from app.models.evidence import Evidence
+from app.models.intel import IntelItem
+from app.models.audit import AuditLog
+from app.models.enums import TechniqueStatus, TestState, TestResult
+
+__all__ = [
+    "User", "Technique", "Test", "Evidence", "IntelItem", "AuditLog",
+    "TechniqueStatus", "TestState", "TestResult"
+]
diff --git a/backend/app/models/audit.py b/backend/app/models/audit.py
new file mode 100644
index 0000000..088ae9a
--- /dev/null
+++ b/backend/app/models/audit.py
@@ -0,0 +1,29 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Column, String, DateTime, ForeignKey
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from sqlalchemy.orm import relationship
+
+from app.database import Base
+
+
+class AuditLog(Base):
+    """
+    Audit log model for tracking all system actions.
+    
+    Records user actions, entity changes, and system events
+    for security auditing and compliance purposes.
+    """
+    __tablename__ = "audit_logs"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    user_id = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=True)
+    action = Column(String, nullable=False)
+    entity_type = Column(String, nullable=True)
+    entity_id = Column(String, nullable=True)
+    timestamp = Column(DateTime, default=datetime.utcnow)
+    details = Column(JSONB, nullable=True)
+
+    # Relationships
+    user = relationship("User")
diff --git a/backend/app/models/enums.py b/backend/app/models/enums.py
new file mode 100644
index 0000000..48f7a5e
--- /dev/null
+++ b/backend/app/models/enums.py
@@ -0,0 +1,23 @@
+import enum
+
+
+class TechniqueStatus(str, enum.Enum):
+    not_evaluated = "not_evaluated"
+    in_progress = "in_progress"
+    validated = "validated"
+    partial = "partial"
+    not_covered = "not_covered"
+    review_required = "review_required"
+
+
+class TestState(str, enum.Enum):
+    draft = "draft"
+    in_review = "in_review"
+    validated = "validated"
+    rejected = "rejected"
+
+
+class TestResult(str, enum.Enum):
+    detected = "detected"
+    not_detected = "not_detected"
+    partially_detected = "partially_detected"
diff --git a/backend/app/models/evidence.py b/backend/app/models/evidence.py
new file mode 100644
index 0000000..91ef600
--- /dev/null
+++ b/backend/app/models/evidence.py
@@ -0,0 +1,30 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Column, String, DateTime, ForeignKey
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+
+from app.database import Base
+
+
+class Evidence(Base):
+    """
+    Evidence model for storing file metadata associated with tests.
+    
+    Files are stored in MinIO, and this model tracks the file location,
+    integrity hash, and upload metadata.
+    """
+    __tablename__ = "evidences"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    test_id = Column(UUID(as_uuid=True), ForeignKey("tests.id"), nullable=False)
+    file_name = Column(String, nullable=False)
+    file_path = Column(String, nullable=False)  # Path in MinIO
+    sha256_hash = Column(String, nullable=False)
+    uploaded_by = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=True)
+    uploaded_at = Column(DateTime, default=datetime.utcnow)
+
+    # Relationships
+    test = relationship("Test", back_populates="evidences")
+    uploader = relationship("User", foreign_keys=[uploaded_by])
diff --git a/backend/app/models/intel.py b/backend/app/models/intel.py
new file mode 100644
index 0000000..9e99a0a
--- /dev/null
+++ b/backend/app/models/intel.py
@@ -0,0 +1,29 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Column, String, Boolean, DateTime, ForeignKey
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+
+from app.database import Base
+
+
+class IntelItem(Base):
+    """
+    Intelligence item model for tracking threat intelligence related to techniques.
+    
+    Stores URLs and metadata from automated intel scans that may indicate
+    new attack variations or detection bypasses for specific techniques.
+    """
+    __tablename__ = "intel_items"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    technique_id = Column(UUID(as_uuid=True), ForeignKey("techniques.id"), nullable=True)
+    url = Column(String, nullable=False)
+    title = Column(String, nullable=True)
+    source = Column(String, nullable=True)
+    detected_at = Column(DateTime, default=datetime.utcnow)
+    reviewed = Column(Boolean, default=False)
+
+    # Relationships
+    technique = relationship("Technique")
diff --git a/backend/app/models/technique.py b/backend/app/models/technique.py
new file mode 100644
index 0000000..f2b9cb2
--- /dev/null
+++ b/backend/app/models/technique.py
@@ -0,0 +1,39 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Column, String, Text, Boolean, DateTime, Enum
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from sqlalchemy.orm import relationship
+
+from app.database import Base
+from app.models.enums import TechniqueStatus
+
+
+class Technique(Base):
+    """
+    MITRE ATT&CK Technique model.
+    
+    Represents an attack technique from the MITRE ATT&CK framework,
+    including its coverage status and associated tests.
+    """
+    __tablename__ = "techniques"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    mitre_id = Column(String, unique=True, nullable=False)  # e.g., "T1059.001"
+    name = Column(String, nullable=False)
+    description = Column(Text, nullable=True)
+    tactic = Column(String, nullable=True)
+    platforms = Column(JSONB, nullable=True, default=[])
+    mitre_version = Column(String, nullable=True)
+    mitre_last_modified = Column(DateTime, nullable=True)
+    is_subtechnique = Column(Boolean, default=False)
+    parent_mitre_id = Column(String, nullable=True)
+    status_global = Column(
+        Enum(TechniqueStatus, name="techniquestatus"),
+        default=TechniqueStatus.not_evaluated
+    )
+    review_required = Column(Boolean, default=False)
+    last_review_date = Column(DateTime, nullable=True)
+
+    # Relationships
+    tests = relationship("Test", back_populates="technique")
diff --git a/backend/app/models/test.py b/backend/app/models/test.py
new file mode 100644
index 0000000..663f854
--- /dev/null
+++ b/backend/app/models/test.py
@@ -0,0 +1,40 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Column, String, Text, DateTime, ForeignKey, Enum
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+
+from app.database import Base
+from app.models.enums import TestState, TestResult
+
+
+class Test(Base):
+    """
+    Test model representing a security test for a MITRE ATT&CK technique.
+    
+    Each test documents an attempt to validate coverage of a specific technique,
+    including the procedure, tools used, and outcome.
+    """
+    __tablename__ = "tests"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    technique_id = Column(UUID(as_uuid=True), ForeignKey("techniques.id"), nullable=False)
+    name = Column(String, nullable=False)
+    description = Column(Text, nullable=True)
+    platform = Column(String, nullable=True)
+    procedure_text = Column(Text, nullable=True)
+    tool_used = Column(String, nullable=True)
+    execution_date = Column(DateTime, nullable=True)
+    created_by = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=True)
+    result = Column(Enum(TestResult, name="testresult"), nullable=True)
+    state = Column(Enum(TestState, name="teststate"), default=TestState.draft)
+    validated_by = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=True)
+    validated_at = Column(DateTime, nullable=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+
+    # Relationships
+    technique = relationship("Technique", back_populates="tests")
+    evidences = relationship("Evidence", back_populates="test")
+    creator = relationship("User", foreign_keys=[created_by])
+    validator = relationship("User", foreign_keys=[validated_by])
diff --git a/backend/app/models/user.py b/backend/app/models/user.py
new file mode 100644
index 0000000..a60fe32
--- /dev/null
+++ b/backend/app/models/user.py
@@ -0,0 +1,31 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Column, String, Boolean, DateTime
+from sqlalchemy.dialects.postgresql import UUID
+
+from app.database import Base
+
+
+class User(Base):
+    """
+    User model for authentication and authorization.
+    
+    Possible roles:
+    - admin: Full system access
+    - red_tech: Red team technician - can create and edit tests
+    - blue_tech: Blue team technician - can create and edit tests
+    - red_lead: Red team lead - can validate tests
+    - blue_lead: Blue team lead - can validate tests
+    - viewer: Read-only access (default)
+    """
+    __tablename__ = "users"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    username = Column(String, unique=True, nullable=False)
+    email = Column(String, nullable=True)
+    hashed_password = Column(String, nullable=False)
+    role = Column(String, nullable=False, default="viewer")
+    is_active = Column(Boolean, default=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+    last_login = Column(DateTime, nullable=True)
diff --git a/backend/app/services/__init__.py b/backend/app/services/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/backend/app/services/audit_service.py b/backend/app/services/audit_service.py
new file mode 100644
index 0000000..099bcd1
--- /dev/null
+++ b/backend/app/services/audit_service.py
@@ -0,0 +1,33 @@
+from sqlalchemy.orm import Session
+
+from app.models.audit import AuditLog
+
+
+def log_action(
+    db: Session,
+    user_id,
+    action: str,
+    entity_type: str = None,
+    entity_id: str = None,
+    details: dict = None
+):
+    """
+    Log an action to the audit log.
+    
+    Args:
+        db: Database session
+        user_id: UUID of the user performing the action (can be None for system actions)
+        action: Description of the action (e.g., "create_test", "validate_technique")
+        entity_type: Type of entity affected (e.g., "technique", "test", "user")
+        entity_id: ID of the entity affected
+        details: Additional details as a dictionary (stored as JSONB)
+    """
+    log = AuditLog(
+        user_id=user_id,
+        action=action,
+        entity_type=entity_type,
+        entity_id=str(entity_id) if entity_id else None,
+        details=details,
+    )
+    db.add(log)
+    db.commit()