diff --git a/alembic/versions/596bb368fc0d_add_orcid_id_to_users.py b/alembic/versions/596bb368fc0d_add_orcid_id_to_users.py
new file mode 100644
index 0000000..6837c41
--- /dev/null
+++ b/alembic/versions/596bb368fc0d_add_orcid_id_to_users.py
@@ -0,0 +1,31 @@
+"""Add orcid_id column to users
+
+Revision ID: 596bb368fc0d
+Revises: d3a7b8c1e2f4
+Create Date: 2026-03-28
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+revision: str = "596bb368fc0d"
+down_revision: Union[str, Sequence[str], None] = "d3a7b8c1e2f4"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "users",
+        sa.Column("orcid_id", sa.String(20), nullable=True),
+    )
+    op.create_index("ix_users_orcid_id", "users", ["orcid_id"], unique=True)
+
+
+def downgrade() -> None:
+    op.drop_index("ix_users_orcid_id", table_name="users")
+    op.drop_column("users", "orcid_id")
diff --git a/app/models/user.py b/app/models/user.py
index 8dad6f0..5313f91 100644
--- a/app/models/user.py
+++ b/app/models/user.py
@@ -1,12 +1,27 @@
 from datetime import datetime, timezone
+import re
 import uuid
 
 from sqlalchemy import Boolean, Column, DateTime, String, TypeDecorator
 from sqlalchemy.dialects.postgresql import UUID
-from sqlalchemy.orm import relationship
+from sqlalchemy.orm import relationship, validates
 
 from app.database import Base
 
+ORCID_PATTERN = re.compile(r"^\d{4}-\d{4}-\d{4}-\d{3}[\dX]$")
+
+
+def validate_orcid_id(value: str | None) -> str | None:
+    """Validate ORCID iD format: XXXX-XXXX-XXXX-XXXX (last char may be X checksum)."""
+    if value is None:
+        return None
+    if not ORCID_PATTERN.match(value):
+        raise ValueError(
+            f"Invalid ORCID iD format: '{value}'. "
+            "Expected format: 0000-0002-1234-5678"
+        )
+    return value
+
 
 # Cross-platform UUID type that works with SQLite
 class GUID(TypeDecorator):
@@ -58,11 +73,16 @@ class User(Base):
         onupdate=lambda: datetime.now(timezone.utc),
         nullable=False,
     )
+    orcid_id = Column(String(20), nullable=True, unique=True, index=True)
 
     # Relationships
     scrolls = relationship("Scroll", back_populates="user")
     sessions = relationship("Session", back_populates="user")
     tokens = relationship("Token", back_populates="user")
 
+    @validates("orcid_id")
+    def _validate_orcid_id(self, _key: str, value: str | None) -> str | None:
+        return validate_orcid_id(value)
+
     def __repr__(self):
         return f"<User(email='{self.email}', display_name='{self.display_name}')>"
diff --git a/tests/test_orcid.py b/tests/test_orcid.py
new file mode 100644
index 0000000..f40283d
--- /dev/null
+++ b/tests/test_orcid.py
@@ -0,0 +1,154 @@
+"""Tests for ORCID iD storage on the User model."""
+
+import pytest
+import pytest_asyncio
+from sqlalchemy import select
+from sqlalchemy.exc import IntegrityError
+
+from app.models.user import User, validate_orcid_id
+
+
+class TestValidateOrcidId:
+    """Tests for the orcid_id format validation function."""
+
+    def test_valid_orcid(self):
+        assert validate_orcid_id("0000-0002-1234-5678") == "0000-0002-1234-5678"
+
+    def test_valid_orcid_with_checksum_x(self):
+        assert validate_orcid_id("0000-0002-1234-567X") == "0000-0002-1234-567X"
+
+    def test_none_passes_through(self):
+        assert validate_orcid_id(None) is None
+
+    def test_rejects_missing_hyphens(self):
+        with pytest.raises(ValueError, match="ORCID"):
+            validate_orcid_id("0000000212345678")
+
+    def test_rejects_too_short(self):
+        with pytest.raises(ValueError, match="ORCID"):
+            validate_orcid_id("0000-0002-1234")
+
+    def test_rejects_letters_in_body(self):
+        with pytest.raises(ValueError, match="ORCID"):
+            validate_orcid_id("000A-0002-1234-5678")
+
+    def test_rejects_empty_string(self):
+        with pytest.raises(ValueError, match="ORCID"):
+            validate_orcid_id("")
+
+    def test_rejects_lowercase_x(self):
+        with pytest.raises(ValueError, match="ORCID"):
+            validate_orcid_id("0000-0002-1234-567x")
+
+
+@pytest.mark.asyncio
+class TestUserOrcidColumn:
+    """Tests for the orcid_id column on the User model."""
+
+    async def test_user_created_without_orcid(self, test_db):
+        """Backward compat: users can be created with no orcid_id."""
+        from app.auth.utils import get_password_hash
+
+        user = User(
+            email="noorcid@example.com",
+            password_hash=get_password_hash("password123"),
+            display_name="No ORCID User",
+            email_verified=True,
+        )
+        test_db.add(user)
+        await test_db.commit()
+        await test_db.refresh(user)
+
+        assert user.orcid_id is None
+
+    async def test_user_created_with_valid_orcid(self, test_db):
+        from app.auth.utils import get_password_hash
+
+        user = User(
+            email="orcid@example.com",
+            password_hash=get_password_hash("password123"),
+            display_name="ORCID User",
+            email_verified=True,
+            orcid_id="0000-0002-1234-5678",
+        )
+        test_db.add(user)
+        await test_db.commit()
+        await test_db.refresh(user)
+
+        assert user.orcid_id == "0000-0002-1234-5678"
+
+    async def test_orcid_with_checksum_x(self, test_db):
+        from app.auth.utils import get_password_hash
+
+        user = User(
+            email="orcidx@example.com",
+            password_hash=get_password_hash("password123"),
+            display_name="ORCID X User",
+            email_verified=True,
+            orcid_id="0000-0002-1234-567X",
+        )
+        test_db.add(user)
+        await test_db.commit()
+        await test_db.refresh(user)
+
+        assert user.orcid_id == "0000-0002-1234-567X"
+
+    async def test_orcid_uniqueness_constraint(self, test_db):
+        """Two users cannot share the same ORCID iD."""
+        from app.auth.utils import get_password_hash
+
+        user1 = User(
+            email="user1@example.com",
+            password_hash=get_password_hash("password123"),
+            display_name="User 1",
+            email_verified=True,
+            orcid_id="0000-0002-1234-5678",
+        )
+        test_db.add(user1)
+        await test_db.commit()
+
+        user2 = User(
+            email="user2@example.com",
+            password_hash=get_password_hash("password123"),
+            display_name="User 2",
+            email_verified=True,
+            orcid_id="0000-0002-1234-5678",
+        )
+        test_db.add(user2)
+
+        with pytest.raises(IntegrityError):
+            await test_db.commit()
+
+    async def test_multiple_users_with_null_orcid(self, test_db):
+        """Multiple users can have NULL orcid_id (no false unique violation)."""
+        from app.auth.utils import get_password_hash
+
+        for i in range(3):
+            user = User(
+                email=f"null_orcid_{i}@example.com",
+                password_hash=get_password_hash("password123"),
+                display_name=f"Null ORCID {i}",
+                email_verified=True,
+            )
+            test_db.add(user)
+
+        await test_db.commit()
+
+        result = await test_db.execute(
+            select(User).where(User.orcid_id.is_(None))
+        )
+        users = result.scalars().all()
+        assert len(users) == 3
+
+    async def test_invalid_orcid_rejected_by_validator(self, test_db):
+        """The @validates decorator rejects bad formats before hitting the DB."""
+        from app.auth.utils import get_password_hash
+
+        with pytest.raises(ValueError, match="ORCID"):
+            User(
+                email="bad@example.com",
+                password_hash=get_password_hash("password123"),
+                display_name="Bad ORCID",
+                email_verified=True,
+                orcid_id="not-an-orcid",
+            )