diff --git a/platform/core/src/index.js b/platform/core/src/index.js
index 9ffa1c70a..acfdd3fbf 100644
--- a/platform/core/src/index.js
+++ b/platform/core/src/index.js
@@ -30,8 +30,9 @@ import {
   //
   DicomMetadataStore,
   DisplaySetService,
-  ToolBarSerivce,
+  ToolBarSerivce, // TODO: Typo
   MeasurementService,
+  ViewportGridService,
 } from './services';
 
 import IWebApiDataSource from './DataSources/IWebApiDataSource';
@@ -70,7 +71,8 @@ const OHIF = {
   UIViewportDialogService,
   DisplaySetService,
   MeasurementService,
-  ToolBarSerivce,
+  ToolBarSerivce, // TODO: TYPO
+  ViewportGridService,
   IWebApiDataSource,
   DicomMetadataStore,
   //
@@ -112,6 +114,7 @@ export {
   DisplaySetService,
   MeasurementService,
   ToolBarSerivce,
+  ViewportGridService,
   IWebApiDataSource,
   DicomMetadataStore,
   ViewModelProvider,
diff --git a/platform/core/src/services/ViewportGridService/ViewportGridService.js b/platform/core/src/services/ViewportGridService/ViewportGridService.js
new file mode 100644
index 000000000..b4b213969
--- /dev/null
+++ b/platform/core/src/services/ViewportGridService/ViewportGridService.js
@@ -0,0 +1,54 @@
+const name = 'ViewportGridService';
+
+const publicAPI = {
+  name,
+  hide: _hide,
+  show: _show,
+  setServiceImplementation,
+};
+
+const serviceImplementation = {
+  _hide: () => console.warn('hide() NOT IMPLEMENTED'),
+  _show: () => console.warn('show() NOT IMPLEMENTED'),
+};
+
+function _show({ viewportIndex, type, message, actions, onSubmit }) {
+  return serviceImplementation._show({
+    viewportIndex,
+    type,
+    message,
+    actions,
+    onSubmit,
+  });
+}
+
+function _hide() {
+  return serviceImplementation._hide();
+}
+
+function setServiceImplementation({
+  hide: hideImplementation,
+  show: showImplementation,
+}) {
+  if (hideImplementation) {
+    serviceImplementation._hide = hideImplementation;
+  }
+  if (showImplementation) {
+    serviceImplementation._show = showImplementation;
+  }
+}
+
+export default {
+  name,
+  create: ({ configuration = {} }) => {
+    return publicAPI;
+  },
+};
+
+// initialState={{
+//   numRows: 1,
+//   numCols: 1,
+//   viewports: [],
+//   activeViewportIndex: 0,
+// }}
+// reducer={viewportGridReducer}
diff --git a/platform/core/src/services/ViewportGridService/index.js b/platform/core/src/services/ViewportGridService/index.js
index e69de29bb..47d083531 100644
--- a/platform/core/src/services/ViewportGridService/index.js
+++ b/platform/core/src/services/ViewportGridService/index.js
@@ -0,0 +1,3 @@
+import ViewportGridService from './ViewportGridService';
+
+export default ViewportGridService;
diff --git a/platform/core/src/services/index.js b/platform/core/src/services/index.js
index 96ecfb4d5..3862a2554 100644
--- a/platform/core/src/services/index.js
+++ b/platform/core/src/services/index.js
@@ -7,6 +7,7 @@ import UIViewportDialogService from './UIViewportDialogService';
 import DicomMetadataStore from './DicomMetadataStore';
 import DisplaySetService from './DisplaySetService';
 import ToolBarSerivce from './ToolBarService';
+import ViewportGridService from './ViewportGridService';
 
 export {
   MeasurementService,
@@ -18,4 +19,5 @@ export {
   DicomMetadataStore,
   DisplaySetService,
   ToolBarSerivce,
+  ViewportGridService,
 };
diff --git a/platform/ui/src/contextProviders/ViewportGridProvider.jsx b/platform/ui/src/contextProviders/ViewportGridProvider.jsx
index c56268cc4..b718d5145 100644
--- a/platform/ui/src/contextProviders/ViewportGridProvider.jsx
+++ b/platform/ui/src/contextProviders/ViewportGridProvider.jsx
@@ -1,20 +1,141 @@
-import React, { createContext, useContext, useReducer } from 'react';
-
-// export const VIEWPORT_GRID_DEFAULT_VALUE = {
-//   numCols: 1,
-//   numRows: 1,
-//   activeViewportIndex: 0,
-//   viewports: [],
-// };
+import React, {
+  createContext,
+  useCallback,
+  useContext,
+  useEffect,
+  useReducer,
+} from 'react';
+import PropTypes from 'prop-types';
 
 export const ViewportGridContext = createContext();
 
-export function ViewportGridProvider({ reducer, initialState, children }) {
+// export function ViewportGridProvider({ reducer, initialState, children }) {
+//   return (
+//     <ViewportGridContext.Provider value={useReducer(reducer, initialState)}>
+//       {children}
+//     </ViewportGridContext.Provider>
+//   );
+// }
+
+export function ViewportGridProvider({ children, service }) {
+  const DEFAULT_STATE = {
+    numRows: 1,
+    numCols: 1,
+    viewports: [],
+    activeViewportIndex: 0,
+  };
+
+  const viewportGridReducer = (state, action) => {
+    switch (action.type) {
+      case 'SET_ACTIVE_VIEWPORT_INDEX':
+        return { ...state, ...{ activeViewportIndex: action.payload } };
+      case 'SET_DISPLAYSET_FOR_VIEWPORT': {
+        const { viewportIndex, displaySetInstanceUID } = action.payload;
+        const viewports = state.viewports.slice();
+
+        viewports[viewportIndex] = { displaySetInstanceUID };
+
+        return { ...state, ...{ viewports } };
+      }
+      case 'SET_LAYOUT': {
+        const { numCols, numRows } = action.payload;
+        const numPanes = numCols * numRows;
+        const viewports = state.viewports.slice();
+        const activeViewportIndex =
+          state.activeViewportIndex >= numPanes ? 0 : state.activeViewportIndex;
+
+        while (viewports.length < numPanes) {
+          viewports.push({});
+        }
+        while (viewports.length > numPanes) {
+          viewports.pop();
+        }
+
+        return {
+          ...state,
+          ...{ activeViewportIndex, numCols, numRows, viewports },
+        };
+      }
+      default:
+        return action.payload;
+    }
+  };
+
+  const [viewportGridState, dispatch] = useReducer(
+    DEFAULT_STATE,
+    viewportGridReducer
+  );
+
+  const getState = useCallback(() => viewportGridState, [viewportGridState]);
+  const setActiveViewportIndex = useCallback(
+    index => dispatch({ type: 'SET_ACTIVE_VIEWPORT_INDEX', payload: index }),
+    [dispatch]
+  );
+  const setDisplaysetForViewport = useCallback(
+    ({ viewportIndex, displaySetInstanceUID }) =>
+      dispatch({
+        type: 'SET_DISPLAYSET_FOR_VIEWPORT',
+        payload: {
+          viewportIndex,
+          displaySetInstanceUID,
+        },
+      }),
+    [dispatch]
+  );
+
+  const setLayout = useCallback(
+    ({ numCols, numRows }) =>
+      dispatch({
+        type: 'SET_LAYOUT',
+        payload: {
+          numCols,
+          numRows,
+        },
+      }),
+    [dispatch]
+  );
+
+  /**
+   * Sets the implementation of a modal service that can be used by extensions.
+   *
+   * @returns void
+   */
+  useEffect(() => {
+    if (service) {
+      service.setServiceImplementation({
+        getState,
+        setActiveViewportIndex,
+        setDisplaysetForViewport,
+        setLayout,
+      });
+    }
+  }, [
+    getState,
+    service,
+    setActiveViewportIndex,
+    setDisplaysetForViewport,
+    setLayout,
+  ]);
+
+  const api = {
+    // getState,
+    setActiveViewportIndex,
+    setDisplaysetForViewport,
+    setLayout,
+  };
+
   return (
-    <ViewportGridContext.Provider value={useReducer(reducer, initialState)}>
+    <ViewportGridContext.Provider value={[viewportGridState, api]}>
       {children}
     </ViewportGridContext.Provider>
   );
 }
 
+ViewportGridProvider.propTypes = {
+  children: PropTypes.any,
+  service: PropTypes.shape({
+    setServiceImplementation: PropTypes.func,
+  }).isRequired,
+};
+
 export const useViewportGrid = () => useContext(ViewportGridContext);
diff --git a/platform/viewer/src/App.jsx b/platform/viewer/src/App.jsx
index 969977107..01f1e3a3d 100644
--- a/platform/viewer/src/App.jsx
+++ b/platform/viewer/src/App.jsx
@@ -54,60 +54,14 @@ function App({ config, defaultExtensions }) {
     UIModalService,
     UINotificationService,
     UIViewportDialogService,
+    ViewportGridService, // TODO: Should this be a "UI" Service?
   } = servicesManager.services;
 
-  // A UI Service may need to use the ViewportGrid context
-  const viewportGridReducer = (state, action) => {
-    console.log(state, action);
-
-    switch (action.type) {
-      case 'SET_ACTIVE_VIEWPORT_INDEX':
-        return { ...state, ...{ activeViewportIndex: action.payload } };
-      case 'SET_DISPLAYSET_FOR_VIEWPORT': {
-        const { viewportIndex, displaySetInstanceUID } = action.payload;
-        const viewports = state.viewports.slice();
-
-        viewports[viewportIndex] = { displaySetInstanceUID };
-
-        return { ...state, ...{ viewports } };
-      }
-      case 'SET_LAYOUT': {
-        const { numCols, numRows } = action.payload;
-        const numPanes = numCols * numRows;
-        const viewports = state.viewports.slice();
-        const activeViewportIndex =
-          state.activeViewportIndex >= numPanes ? 0 : state.activeViewportIndex;
-
-        while (viewports.length < numPanes) {
-          viewports.push({});
-        }
-        while (viewports.length > numPanes) {
-          viewports.pop();
-        }
-
-        return {
-          ...state,
-          ...{ activeViewportIndex, numCols, numRows, viewports },
-        };
-      }
-      default:
-        return action.payload;
-    }
-  };
-
   return (
     <AppConfigProvider value={appConfigState}>
       <Router basename={routerBasename}>
         <ThemeWrapper>
-          <ViewportGridProvider
-            initialState={{
-              numRows: 1,
-              numCols: 1,
-              viewports: [],
-              activeViewportIndex: 0,
-            }}
-            reducer={viewportGridReducer}
-          >
+          <ViewportGridProvider service={ViewportGridService}>
             <ViewportDialogProvider service={UIViewportDialogService}>
               <SnackbarProvider service={UINotificationService}>
                 <DialogProvider service={UIDialogService}>
diff --git a/platform/viewer/src/appInit.js b/platform/viewer/src/appInit.js
index ef8c16641..2f5433f54 100644
--- a/platform/viewer/src/appInit.js
+++ b/platform/viewer/src/appInit.js
@@ -10,6 +10,7 @@ import {
   MeasurementService,
   DisplaySetService,
   ToolBarSerivce,
+  ViewportGridService,
   // utils,
   // redux as reduxOHIF,
 } from '@ohif/core';
@@ -51,6 +52,7 @@ function appInit(appConfigOrFunc, defaultExtensions) {
     MeasurementService,
     DisplaySetService,
     ToolBarSerivce,
+    ViewportGridService,
   ]);
 
   /**