diff --git a/alembic/versions/25bcba9b99a9_add_invitiations.py b/alembic/versions/25bcba9b99a9_add_invitiations.py
new file mode 100644
index 00000000..c2681435
--- /dev/null
+++ b/alembic/versions/25bcba9b99a9_add_invitiations.py
@@ -0,0 +1,42 @@
+"""add invitiations
+
+Revision ID: 25bcba9b99a9
+Revises: c99026ab9918
+Create Date: 2018-10-23 15:03:12.641069
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision = '25bcba9b99a9'
+down_revision = 'c99026ab9918'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('invitations',
+    sa.Column('time_created', sa.TIMESTAMP(timezone=True), server_default=sa.text('now()'), nullable=False),
+    sa.Column('time_updated', sa.TIMESTAMP(timezone=True), server_default=sa.text('now()'), nullable=False),
+    sa.Column('id', postgresql.UUID(as_uuid=True), server_default=sa.text('uuid_generate_v4()'), nullable=False),
+    sa.Column('user_id', postgresql.UUID(as_uuid=True), nullable=True),
+    sa.Column('workspace_id', postgresql.UUID(as_uuid=True), nullable=True),
+    sa.Column('valid', sa.Boolean(), nullable=True),
+    sa.ForeignKeyConstraint(['user_id'], ['users.id'], ),
+    sa.ForeignKeyConstraint(['workspace_id'], ['workspaces.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_invitations_user_id'), 'invitations', ['user_id'], unique=False)
+    op.create_index(op.f('ix_invitations_workspace_id'), 'invitations', ['workspace_id'], unique=False)
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f('ix_invitations_workspace_id'), table_name='invitations')
+    op.drop_index(op.f('ix_invitations_user_id'), table_name='invitations')
+    op.drop_table('invitations')
+    # ### end Alembic commands ###
diff --git a/atst/domain/invitations.py b/atst/domain/invitations.py
new file mode 100644
index 00000000..2f067b36
--- /dev/null
+++ b/atst/domain/invitations.py
@@ -0,0 +1,62 @@
+import datetime
+from sqlalchemy.orm.exc import NoResultFound
+
+from atst.database import db
+from atst.models import Invitation
+
+from .exceptions import NotFoundError
+
+
+class InvitationExpired(Exception):
+    def __init__(self, invite_id):
+        self.invite_id = invite_id
+
+    @property
+    def message(self):
+        return "{} has expired".format(self.invite_id)
+
+
+class Invitations(object):
+    EXPIRATION_LIMIT = 360
+
+    @classmethod
+    def _get(cls, invite_id):
+        try:
+            invite = db.session.query(Invitation).filter_by(id=invite_id).one()
+        except NoResultFound:
+            raise NotFoundError("invite")
+
+        return invite
+
+    @classmethod
+    def create(cls, workspace, user):
+        invite = Invitation(workspace=workspace, user=user, valid=True)
+        db.session.add(invite)
+        db.session.commit()
+
+        return invite
+
+    @classmethod
+    def accept(cls, invite_id):
+        invite = Invitations._get(invite_id)
+        valid = Invitations._is_valid(invite)
+
+        invite.valid = False
+        db.session.add(invite)
+        db.session.commit()
+
+        if not valid:
+            raise InvitationExpired(invite_id)
+
+        return invite
+
+    @classmethod
+    def _is_valid(cls, invite):
+        if not invite.valid:
+            return False
+        else:
+            time_created = invite.time_created
+            expiration = datetime.datetime.now(
+                time_created.tzinfo
+            ) - datetime.timedelta(minutes=Invitations.EXPIRATION_LIMIT)
+            return invite.time_created > expiration
diff --git a/atst/models/__init__.py b/atst/models/__init__.py
index 91cee016..27afc327 100644
--- a/atst/models/__init__.py
+++ b/atst/models/__init__.py
@@ -18,3 +18,4 @@ from .request_revision import RequestRevision
 from .request_review import RequestReview
 from .request_internal_comment import RequestInternalComment
 from .audit_event import AuditEvent
+from .invitation import Invitation
diff --git a/atst/models/invitation.py b/atst/models/invitation.py
new file mode 100644
index 00000000..97158370
--- /dev/null
+++ b/atst/models/invitation.py
@@ -0,0 +1,25 @@
+from sqlalchemy import Column, ForeignKey, Boolean
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+
+from atst.models import Base, types
+from atst.models.mixins.timestamps import TimestampsMixin
+
+
+class Invitation(Base, TimestampsMixin):
+    __tablename__ = "invitations"
+
+    id = types.Id()
+
+    user_id = Column(UUID(as_uuid=True), ForeignKey("users.id"), index=True)
+    user = relationship("User", backref="invitations")
+
+    workspace_id = Column(UUID(as_uuid=True), ForeignKey("workspaces.id"), index=True)
+    workspace = relationship("Workspace", backref="invitations")
+
+    valid = Column(Boolean, default=True)
+
+    def __repr__(self):
+        return "<Invitation(user='{}', workspace='{}', id='{}')>".format(
+            self.user.id, self.workspace.id, self.id
+        )
diff --git a/tests/domain/test_invitations.py b/tests/domain/test_invitations.py
new file mode 100644
index 00000000..b755bc3a
--- /dev/null
+++ b/tests/domain/test_invitations.py
@@ -0,0 +1,48 @@
+import datetime
+import pytest
+
+from atst.domain.invitations import Invitations, InvitationExpired
+
+from tests.factories import WorkspaceFactory, UserFactory, InvitationFactory
+
+
+def test_create_invitation():
+    workspace = WorkspaceFactory.create()
+    user = UserFactory.create()
+    invite = Invitations.create(workspace, user)
+    assert invite.user == user
+    assert invite.workspace == workspace
+    assert invite.valid
+
+
+def test_accept_invitation():
+    workspace = WorkspaceFactory.create()
+    user = UserFactory.create()
+    invite = Invitations.create(workspace, user)
+    assert invite.valid
+    accepted_invite = Invitations.accept(invite.id)
+    assert not accepted_invite.valid
+
+
+def test_accept_expired_invitation():
+    workspace = WorkspaceFactory.create()
+    user = UserFactory.create()
+    increment = Invitations.EXPIRATION_LIMIT + 1
+    created_at = datetime.datetime.now() - datetime.timedelta(minutes=increment)
+    invite = InvitationFactory.create(
+        workspace_id=workspace.id, user_id=user.id, time_created=created_at, valid=True
+    )
+    with pytest.raises(InvitationExpired):
+        Invitations.accept(invite.id)
+
+    assert not invite.valid
+
+
+def test_accept_invalid_invite():
+    workspace = WorkspaceFactory.create()
+    user = UserFactory.create()
+    invite = InvitationFactory.create(
+        workspace_id=workspace.id, user_id=user.id, valid=False
+    )
+    with pytest.raises(InvitationExpired):
+        Invitations.accept(invite.id)
diff --git a/tests/factories.py b/tests/factories.py
index b2338a06..ca40e61c 100644
--- a/tests/factories.py
+++ b/tests/factories.py
@@ -20,6 +20,7 @@ from atst.models.workspace import Workspace
 from atst.domain.roles import Roles
 from atst.models.workspace_role import WorkspaceRole
 from atst.models.environment_role import EnvironmentRole
+from atst.models.invitation import Invitation
 
 
 class Base(factory.alchemy.SQLAlchemyModelFactory):
@@ -325,3 +326,8 @@ class EnvironmentRoleFactory(Base):
     environment = factory.SubFactory(EnvironmentFactory)
     role = factory.Faker("name")
     user = factory.SubFactory(UserFactory)
+
+
+class InvitationFactory(Base):
+    class Meta:
+        model = Invitation