diff --git a/app/__init__.py b/app/__init__.py
index 7cf17d9a9..9eb681237 100644
--- a/app/__init__.py
+++ b/app/__init__.py
@@ -36,7 +36,7 @@ from notifications_utils.formatters import formatted_list
 from werkzeug.exceptions import abort
 from werkzeug.local import LocalProxy
 
-from app import proxy_fix
+from app import proxy_fix, navigation
 from app.config import configs
 from app.asset_fingerprinter import AssetFingerprinter
 from app.notify_client.service_api_client import ServiceAPIClient
@@ -171,6 +171,10 @@ def init_app(application):
     def _attach_current_user():
         return{'current_user': current_user}
 
+    @application.context_processor
+    def _nav_selected():
+        return {'nav_selected': navigation.nav_selected}
+
     @application.before_request
     def record_start_time():
         g.start = monotonic()
diff --git a/app/assets/stylesheets/components/navigation.scss b/app/assets/stylesheets/components/navigation.scss
index 0a059573f..d6c3531d7 100644
--- a/app/assets/stylesheets/components/navigation.scss
+++ b/app/assets/stylesheets/components/navigation.scss
@@ -63,6 +63,15 @@
       color: $text-colour;
     }
 
+    &.selected {
+      @include bold-19;
+      position: relative;
+      // These two lines stop the width of the item jumping so much
+      // between selected and unselected states
+      left: -0.5px;
+      letter-spacing: -0.01em;
+    }
+
   }
 
 }
@@ -99,7 +108,7 @@
 
   &__item--active {
     @include bold-16;
-    
+
     a:link, a:visited {
       color: $text-colour;
     }
diff --git a/app/navigation.py b/app/navigation.py
new file mode 100644
index 000000000..46054eec7
--- /dev/null
+++ b/app/navigation.py
@@ -0,0 +1,238 @@
+from itertools import chain
+
+from flask import request
+
+mapping = {
+    'dashboard': {
+        'conversation',
+        'inbox',
+        'monthly',
+        'service_dashboard',
+        'template_usage',
+        'view_job',
+        'view_jobs',
+        'view_notification',
+        'view_notifications',
+    },
+    'templates': {
+        'action_blocked',
+        'add_service_template',
+        'add_template_by_type',
+        'check_messages',
+        'check_notification',
+        'choose_template',
+        'confirm_redact_template',
+        'conversation_reply',
+        'delete_service_template',
+        'edit_service_template',
+        'send_messages',
+        'send_one_off',
+        'send_one_off_step',
+        'send_test',
+        'send_test_preview',
+        'send_test_step',
+        'set_sender',
+        'set_template_sender',
+        'view_template',
+        'view_template_version',
+        'view_template_versions',
+    },
+    'team-members': {
+        'edit_user_permissions',
+        'invite_user',
+        'manage_users',
+        'remove_user_from_service',
+    },
+    'usage': {
+        'usage',
+    },
+    'settings': {
+        'link_service_to_organisation',
+        'request_to_go_live',
+        'service_add_email_reply_to',
+        'service_add_letter_contact',
+        'service_add_sms_sender',
+        'service_edit_email_reply_to',
+        'service_edit_letter_contact',
+        'service_edit_sms_sender',
+        'service_email_reply_to',
+        'service_letter_contact_details',
+        'service_name_change',
+        'service_name_change_confirm',
+        'service_set_auth_type',
+        'service_set_email',
+        'service_set_email_branding',
+        'service_set_inbound_number',
+        'service_set_inbound_sms',
+        'service_set_international_sms',
+        'service_set_letter_contact_block',
+        'service_set_letters',
+        'service_set_reply_to_email',
+        'service_set_sms',
+        'service_set_sms_prefix',
+        'service_settings',
+        'service_sms_senders',
+        'set_free_sms_allowance',
+        'set_letter_branding',
+        'set_organisation_type',
+        'submit_request_to_go_live',
+    },
+    'api-integration': {
+        'api_callbacks',
+        'api_documentation',
+        'api_integration',
+        'api_keys',
+        'create_api_key',
+        'delivery_status_callback',
+        'received_text_messages_callback',
+        'revoke_api_key',
+        'whitelist',
+    },
+}
+
+exclude = {
+    'accept_invite',
+    'accept_org_invite',
+    'add_organisation',
+    'add_service',
+    'agreement',
+    'archive_service',
+    'bat_phone',
+    'callbacks',
+    'cancel_invited_org_user',
+    'cancel_invited_user',
+    'cancel_job',
+    'check_and_resend_text_code',
+    'check_and_resend_verification_code',
+    'check_messages_preview',
+    'choose_account',
+    'choose_service',
+    'confirm_edit_organisation_name',
+    'conversation_reply_with_template',
+    'conversation_updates',
+    'cookies',
+    'create_email_branding',
+    'delivery_and_failure',
+    'design_content',
+    'documentation',
+    'download_agreement',
+    'download_notifications_csv',
+    'edit_organisation_name',
+    'edit_provider',
+    'edit_user_org_permissions',
+    'email_branding',
+    'email_not_received',
+    'email_template',
+    'error',
+    'features',
+    'feedback',
+    'forgot_password',
+    'get_example_csv',
+    'get_notifications_as_json',
+    'go_to_dashboard_after_tour',
+    'inbound_sms_admin',
+    'inbox_download',
+    'inbox_updates',
+    'index',
+    'information_risk_management',
+    'information_security',
+    'integration_testing',
+    'invite_org_user',
+    'letter_jobs',
+    'live_services',
+    'manage_org_users',
+    'new_password',
+    'old_feedback',
+    'old_integration_testing',
+    'old_roadmap',
+    'old_service_dashboard',
+    'old_submit_feedback',
+    'old_terms',
+    'old_using_notify',
+    'organisation_dashboard',
+    'organisation_settings',
+    'organisations',
+    'platform_admin',
+    'pricing',
+    'redact_template',
+    'register',
+    'register_from_invite',
+    'register_from_org_invite',
+    'registration_continue',
+    'remove_user_from_organisation',
+    'resend_email_link',
+    'resend_email_verification',
+    'resume_service',
+    'roadmap',
+    'security',
+    'send_notification',
+    'service_dashboard_updates',
+    'service_switch_can_send_email',
+    'service_switch_can_send_precompiled_letter',
+    'service_switch_can_send_sms',
+    'service_switch_email_auth',
+    'service_switch_live',
+    'service_switch_research_mode',
+    'services_or_dashboard',
+    'show_accounts_or_dashboard',
+    'sign_in',
+    'sign_out',
+    'start_job',
+    'start_tour',
+    'styleguide',
+    'support',
+    'suspend_service',
+    'temp_service_history',
+    'template_history',
+    'terms',
+    'thanks',
+    'triage',
+    'trial_mode',
+    'trial_services',
+    'two_factor',
+    'two_factor_email',
+    'two_factor_email_sent',
+    'update_email_branding',
+    'user_profile',
+    'user_profile_email',
+    'user_profile_email_authenticate',
+    'user_profile_email_confirm',
+    'user_profile_mobile_number',
+    'user_profile_mobile_number_authenticate',
+    'user_profile_mobile_number_confirm',
+    'user_profile_name',
+    'user_profile_password',
+    'using_notify',
+    'verify',
+    'verify_email',
+    'verify_mobile',
+    'view_job_csv',
+    'view_job_updates',
+    'view_letter_notification_as_preview',
+    'view_letter_template_preview',
+    'view_notification_updates',
+    'view_notifications_csv',
+    'view_provider',
+    'view_providers',
+    'view_template_version_preview',
+}
+
+mapping = {
+    navigation: {
+        'main.{}'.format(endpoint) for endpoint in endpoints
+    } for navigation, endpoints in mapping.items()
+}
+
+endpoints_with_navigation = tuple(chain.from_iterable((
+    endpoints for navigation_item, endpoints in mapping.items()
+)))
+
+endpoints_without_navigation = tuple(
+    'main.{}'.format(endpoint) for endpoint in exclude
+) + ('static', 'status.show_status')
+
+
+def nav_selected(navigation_item):
+    if request.endpoint in mapping[navigation_item]:
+        return "class=selected"
+    return ''
diff --git a/app/templates/main_nav.html b/app/templates/main_nav.html
index ef5039379..91b1883a1 100644
--- a/app/templates/main_nav.html
+++ b/app/templates/main_nav.html
@@ -43,19 +43,19 @@
 {% else %}
 <nav class="navigation">
   <ul>
-    <li><a href="{{ url_for('.service_dashboard', service_id=current_service.id) }}">Dashboard</a></li>
+    <li><a href="{{ url_for('.service_dashboard', service_id=current_service.id) }}" {{ nav_selected('dashboard') }}>Dashboard</a></li>
   {% if current_user.has_permissions('view_activity') %}
-    <li><a href="{{ url_for('.choose_template', service_id=current_service.id) }}">Templates</a></li>
+    <li><a href="{{ url_for('.choose_template', service_id=current_service.id) }}" {{ nav_selected('templates') }}>Templates</a></li>
   {% endif %}
-  <li><a href="{{ url_for('.manage_users', service_id=current_service.id) }}">Team members</a></li>
+  <li><a href="{{ url_for('.manage_users', service_id=current_service.id) }}" {{ nav_selected('team-members') }}>Team members</a></li>
   {% if current_user.has_permissions('manage_service') %}
-    <li><a href="{{ url_for('.usage', service_id=current_service.id) }}">Usage</a></li>
+    <li><a href="{{ url_for('.usage', service_id=current_service.id) }}" {{ nav_selected('usage') }}>Usage</a></li>
   {% endif %}
   {% if current_user.has_permissions('manage_api_keys', 'manage_service') %}
-    <li><a href="{{ url_for('.service_settings', service_id=current_service.id) }}">Settings</a></li>
+    <li><a href="{{ url_for('.service_settings', service_id=current_service.id) }}" {{ nav_selected('settings') }}>Settings</a></li>
   {% endif %}
   {% if current_user.has_permissions('manage_api_keys') %}
-    <li><a href="{{ url_for('.api_integration', service_id=current_service.id) }}">API integration</a></li>
+    <li><a href="{{ url_for('.api_integration', service_id=current_service.id) }}" {{ nav_selected('api-integration') }}>API integration</a></li>
   {% endif %}
   </ul>
 </nav>
diff --git a/tests/app/test_navigation.py b/tests/app/test_navigation.py
new file mode 100644
index 000000000..392593f61
--- /dev/null
+++ b/tests/app/test_navigation.py
@@ -0,0 +1,53 @@
+import pytest
+from tests.conftest import SERVICE_ONE_ID, app_
+
+from app import navigation
+
+all_endpoints = [
+    rule.endpoint for rule in next(app_(None)).url_map.iter_rules()
+]
+
+
+def test_navigation_items_are_properly_defined():
+    for endpoint in navigation.endpoints_with_navigation:
+        assert endpoint in all_endpoints
+        assert endpoint not in navigation.endpoints_without_navigation
+        assert navigation.endpoints_with_navigation.count(endpoint) == 1
+
+
+def test_excluded_navigation_items_are_properly_defined():
+    for endpoint in navigation.endpoints_without_navigation:
+        assert endpoint in all_endpoints
+        assert endpoint not in navigation.endpoints_with_navigation
+        assert navigation.endpoints_without_navigation.count(endpoint) == 1
+
+
+def test_all_endpoints_are_covered():
+    for endpoint in all_endpoints:
+        assert endpoint in (
+            navigation.endpoints_with_navigation +
+            navigation.endpoints_without_navigation
+        )
+
+
+@pytest.mark.xfail(raises=KeyError)
+def test_raises_on_invalid_navigation_item(client_request):
+    navigation.nav_selected('foo')
+
+
+@pytest.mark.parametrize('endpoint, selected_nav_item', [
+    ('main.choose_template', 'Templates'),
+    ('main.manage_users', 'Team members'),
+])
+def test_a_page_should_nave_selected_navigation_item(
+    client_request,
+    mock_get_service_templates,
+    mock_get_users_by_service,
+    mock_get_invites_for_service,
+    endpoint,
+    selected_nav_item,
+):
+    page = client_request.get(endpoint, service_id=SERVICE_ONE_ID)
+    selected_nav_items = page.select('.navigation a.selected')
+    assert len(selected_nav_items) == 1
+    assert selected_nav_items[0].text.strip() == selected_nav_item