diff --git a/alembic/versions/ab1167fc8260_add_user_last_session_id.py b/alembic/versions/ab1167fc8260_add_user_last_session_id.py
new file mode 100644
index 00000000..b1039571
--- /dev/null
+++ b/alembic/versions/ab1167fc8260_add_user_last_session_id.py
@@ -0,0 +1,28 @@
+"""add_user_last_session_id
+
+Revision ID: ab1167fc8260
+Revises: c5deba1826be
+Create Date: 2019-05-15 16:25:48.766451
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision = 'ab1167fc8260'
+down_revision = 'c5deba1826be'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column('users', sa.Column('last_session_id', postgresql.UUID(as_uuid=True), nullable=True))
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column('users', 'last_session_id')
+    # ### end Alembic commands ###
diff --git a/atst/app.py b/atst/app.py
index c729c65a..ccecd534 100644
--- a/atst/app.py
+++ b/atst/app.py
@@ -2,7 +2,7 @@ import os
 import re
 import pathlib
 from configparser import ConfigParser
-from flask import Flask, request, g
+from flask import Flask, request, g, session
 from flask_session import Session
 import redis
 from unipath import Path
@@ -30,6 +30,7 @@ from atst.utils.form_cache import FormCache
 from atst.utils.json import CustomJSONEncoder
 from atst.queue import queue
 from atst.utils.notification_sender import NotificationSender
+from atst.utils.session_limiter import SessionLimiter
 
 from logging.config import dictConfig
 from atst.utils.logging import JsonFormatter, RequestContextFilter
@@ -70,6 +71,7 @@ def make_app(config):
     db.init_app(app)
     csrf.init_app(app)
     Session(app)
+    make_session_limiter(app, session, config)
     assets_environment.init_app(app)
 
     make_error_pages(app)
@@ -162,6 +164,9 @@ def map_config(config):
         "DISABLE_CRL_CHECK": config.getboolean("default", "DISABLE_CRL_CHECK"),
         "CRL_FAIL_OPEN": config.getboolean("default", "CRL_FAIL_OPEN"),
         "LOG_JSON": config.getboolean("default", "LOG_JSON"),
+        "LIMIT_CONCURRENT_SESSIONS": config.getboolean(
+            "default", "LIMIT_CONCURRENT_SESSIONS"
+        ),
     }
 
 
@@ -253,6 +258,10 @@ def make_notification_sender(app):
     app.notification_sender = NotificationSender(queue)
 
 
+def make_session_limiter(app, session, config):
+    app.session_limiter = SessionLimiter(config, session, app.redis)
+
+
 def apply_json_logger():
     dictConfig(
         {
diff --git a/atst/domain/users.py b/atst/domain/users.py
index baf5acb0..daf69c68 100644
--- a/atst/domain/users.py
+++ b/atst/domain/users.py
@@ -89,6 +89,12 @@ class Users(object):
         db.session.add(user)
         db.session.commit()
 
+    @classmethod
+    def update_last_session_id(cls, user, session_id):
+        user.last_session_id = session_id
+        db.session.add(user)
+        db.session.commit()
+
     @classmethod
     def finalize(cls, user):
         user.provisional = False
diff --git a/atst/models/user.py b/atst/models/user.py
index c1693a37..61ba0c79 100644
--- a/atst/models/user.py
+++ b/atst/models/user.py
@@ -58,6 +58,7 @@ class User(
     designation = Column(String)
     date_latest_training = Column(Date)
     last_login = Column(TIMESTAMP(timezone=True), nullable=True)
+    last_session_id = Column(UUID(as_uuid=True), nullable=True)
 
     provisional = Column(Boolean)
 
diff --git a/atst/routes/__init__.py b/atst/routes/__init__.py
index f923517f..94acb897 100644
--- a/atst/routes/__init__.py
+++ b/atst/routes/__init__.py
@@ -8,9 +8,9 @@ from flask import (
     url_for,
     request,
     make_response,
+    current_app as app,
 )
 
-from flask import current_app as app
 from jinja2.exceptions import TemplateNotFound
 import pendulum
 import os
@@ -125,6 +125,7 @@ def redirect_after_login_url():
 def current_user_setup(user):
     session["user_id"] = user.id
     session["last_login"] = user.last_login
+    app.session_limiter.on_login(user)
     Users.update_last_login(user)
 
 
diff --git a/atst/utils/session_limiter.py b/atst/utils/session_limiter.py
new file mode 100644
index 00000000..cae43c5d
--- /dev/null
+++ b/atst/utils/session_limiter.py
@@ -0,0 +1,19 @@
+from atst.domain.users import Users
+
+
+class SessionLimiter(object):
+    def __init__(self, config, session, redis):
+        self.limit_logins = config["LIMIT_CONCURRENT_SESSIONS"]
+        self.session = session
+        self.redis = redis
+
+    def on_login(self, user):
+        if not self.limit_logins:
+            return
+
+        session_id = self.session.sid
+        self._delete_session(user.last_session_id)
+        Users.update_last_session_id(user, session_id)
+
+    def _delete_session(self, session_id):
+        self.redis.delete("session:{}".format(session_id))
diff --git a/config/base.ini b/config/base.ini
index 36f1e0a7..ce98fbf2 100644
--- a/config/base.ini
+++ b/config/base.ini
@@ -34,3 +34,4 @@ STORAGE_SECRET=''
 STORAGE_PROVIDER=LOCAL
 STORAGE_CRL_ARCHIVE_NAME = dod_crls.tar.bz
 WTF_CSRF_ENABLED = true
+LIMIT_CONCURRENT_SESSIONS = false
diff --git a/config/prod.ini b/config/prod.ini
index bbbf8f8b..ebc1dc40 100644
--- a/config/prod.ini
+++ b/config/prod.ini
@@ -1,3 +1,4 @@
 [default]
 SESSION_COOKIE_SECURE=True
 SESSION_COOKIE_DOMAIN=atat.codes
+LIMIT_CONCURRENT_SESSIONS=True
diff --git a/tests/utils/test_logging.py b/tests/utils/test_logging.py
index cb8198d3..fd934d07 100644
--- a/tests/utils/test_logging.py
+++ b/tests/utils/test_logging.py
@@ -2,6 +2,7 @@ from io import StringIO
 import json
 import logging
 from uuid import uuid4
+from unittest.mock import Mock
 
 import pytest
 
@@ -62,13 +63,16 @@ def test_json_formatter_for_exceptions(logger, log_stream_content):
     assert log.get("details")
 
 
-def test_request_context_filter(logger, log_stream_content, request_ctx):
-    user = UserFactory.create()
-    uuid = str(uuid4())
+def test_request_context_filter(logger, log_stream_content, request_ctx, monkeypatch):
+    request_uuid = str(uuid4())
+    user_uuid = str(uuid4())
 
-    request_ctx.g.current_user = user
-    request_ctx.request.environ["HTTP_X_REQUEST_ID"] = uuid
+    user = Mock(spec=["id"])
+    user.id = user_uuid
+
+    monkeypatch.setattr("atst.utils.logging.g", Mock(current_user=user))
+    request_ctx.request.environ["HTTP_X_REQUEST_ID"] = request_uuid
     logger.info("this user is doing something")
     log = json.loads(log_stream_content())
-    assert log["user_id"] == str(user.id)
-    assert log["request_id"] == uuid
+    assert log["user_id"] == str(user_uuid)
+    assert log["request_id"] == request_uuid
diff --git a/tests/utils/test_session_limiter.py b/tests/utils/test_session_limiter.py
new file mode 100644
index 00000000..4595d4e3
--- /dev/null
+++ b/tests/utils/test_session_limiter.py
@@ -0,0 +1,51 @@
+import pytest
+from redis import Redis
+from unittest.mock import Mock
+from uuid import uuid4
+
+from atst.utils.session_limiter import SessionLimiter
+from tests.factories import UserFactory
+from atst.models.user import User
+
+
+@pytest.fixture
+def mock_redis():
+    return Mock(spec=Redis)
+
+
+@pytest.fixture
+def mock_session():
+    mock = Mock(spec=["sid"])
+    mock.sid = uuid4()
+    return mock
+
+
+def test_session_limiter_deletes_users_old_session(mock_redis, mock_session):
+    last_session_id = uuid4()
+    current_session_id = uuid4()
+
+    mock_session.sid = current_session_id
+
+    session_limiter = SessionLimiter(
+        {"LIMIT_CONCURRENT_SESSIONS": True}, mock_session, mock_redis
+    )
+    user = UserFactory.create(last_session_id=last_session_id)
+    session_limiter.on_login(user)
+
+    mock_redis.delete.assert_called_with("session:{}".format(last_session_id))
+
+
+def test_session_limiter_updates_users_last_sesion_id(mock_redis, mock_session, db):
+    last_session_id = uuid4()
+    current_session_id = uuid4()
+
+    mock_session.sid = current_session_id
+
+    session_limiter = SessionLimiter(
+        {"LIMIT_CONCURRENT_SESSIONS": True}, mock_session, mock_redis
+    )
+    user = UserFactory.create(last_session_id=last_session_id)
+    session_limiter.on_login(user)
+
+    user = db.session.query(User).get(user.id)
+    assert user.last_session_id == current_session_id