diff --git a/umap/static/umap/js/modules/global.js b/umap/static/umap/js/modules/global.js
index 813fe651..d158a40b 100644
--- a/umap/static/umap/js/modules/global.js
+++ b/umap/static/umap/js/modules/global.js
@@ -13,31 +13,34 @@ import { AjaxAutocomplete, AjaxAutocompleteMultiple } from './autocomplete.js'
 import Orderable from './orderable.js'
 import Importer from './importer.js'
 import Help from './help.js'
+import { SyncEngine } from './sync/engine.js'
 
 // Import modules and export them to the global scope.
 // For the not yet module-compatible JS out there.
 
+// By alphabetic order
 window.U = {
-  URLs,
-  Request,
-  ServerRequest,
-  RequestError,
-  HTTPError,
-  NOKError,
-  Browser,
-  Facets,
-  Panel,
   Alert,
-  Dialog,
-  Tooltip,
-  EditPanel,
-  FullPanel,
-  Utils,
-  SCHEMA,
-  Importer,
-  Orderable,
-  Caption,
   AjaxAutocomplete,
   AjaxAutocompleteMultiple,
+  Browser,
+  Caption,
+  Dialog,
+  EditPanel,
+  Facets,
+  FullPanel,
   Help,
+  HTTPError,
+  Importer,
+  NOKError,
+  Orderable,
+  Panel,
+  Request,
+  RequestError,
+  SCHEMA,
+  ServerRequest,
+  SyncEngine,
+  Tooltip,
+  URLs,
+  Utils,
 }
diff --git a/umap/static/umap/js/modules/sync/engine.js b/umap/static/umap/js/modules/sync/engine.js
new file mode 100644
index 00000000..7c77ef27
--- /dev/null
+++ b/umap/static/umap/js/modules/sync/engine.js
@@ -0,0 +1,91 @@
+import { WebSocketTransport } from './websocket.js'
+import {
+  MapUpdater,
+  MarkerUpdater,
+  PolygonUpdater,
+  PolylineUpdater,
+  DatalayerUpdater,
+} from './updaters.js'
+
+export class SyncEngine {
+  constructor(map, webSocketURI, authToken) {
+    this.map = map
+    this.receiver = new MessagesDispatcher(this.map)
+    this.transport = new WebSocketTransport(webSocketURI, authToken, this.receiver)
+    this.sender = new MessagesSender(this.transport)
+
+    this.upsert = this.sender.upsert.bind(this.sender)
+    this.update = this.sender.update.bind(this.sender)
+    this.delete = this.sender.delete.bind(this.sender)
+  }
+}
+
+export class MessagesDispatcher {
+  constructor(map) {
+    this.map = map
+    this.updaters = {
+      map: new MapUpdater(this.map),
+      marker: new MarkerUpdater(this.map),
+      polyline: new PolylineUpdater(this.map),
+      polygon: new PolygonUpdater(this.map),
+      datalayer: new DatalayerUpdater(this.map),
+    }
+  }
+
+  getUpdater(subject, metadata) {
+    switch (subject) {
+      case 'feature':
+        const featureTypeExists = Object.keys(this.updaters).includes(
+          metadata.featureType
+        )
+        if (featureTypeExists) {
+          const updater = this.updaters[metadata.featureType]
+          console.log(`found updater ${metadata.featureType}, ${updater}`)
+          return updater
+        }
+      case 'map':
+      case 'datalayer':
+        return this.updaters[subject]
+      default:
+        throw new Error(`Unknown updater ${subject}, ${metadata}`)
+    }
+  }
+
+  dispatch({ kind, payload }) {
+    console.log(kind, payload)
+    if (kind == 'sync-protocol') {
+      let updater = this.getUpdater(payload.subject, payload.metadata)
+      updater.applyMessage(payload)
+    }
+  }
+}
+
+/**
+ * Sends the message to the other party (using the specified transport):
+ *
+ * - `subject` is the type of object this is referering to (map, feature, layer)
+ * - `metadata` contains information about the object we're refering to (id, layerId for instance)
+ * - `key` and
+ * - `value` are the keys and values that are being modified.
+ */
+export class MessagesSender {
+  constructor(transport) {
+    this._transport = transport
+  }
+
+  send(message) {
+    this._transport.send('sync-protocol', message)
+  }
+
+  upsert(subject, metadata, value) {
+    this.send({ verb: 'upsert', subject, metadata, value })
+  }
+
+  update(subject, metadata, key, value) {
+    this.send({ verb: 'update', subject, metadata, key, value })
+  }
+
+  delete(subject, metadata, key) {
+    this.send({ verb: 'delete', subject, metadata, key })
+  }
+}
diff --git a/umap/static/umap/js/modules/sync/updaters.js b/umap/static/umap/js/modules/sync/updaters.js
new file mode 100644
index 00000000..62a13f6a
--- /dev/null
+++ b/umap/static/umap/js/modules/sync/updaters.js
@@ -0,0 +1,131 @@
+/**
+ * This file contains the updaters: classes that are able to convert messages
+ * received from another party (or the server) to changes on the map.
+ */
+
+class BaseUpdater {
+  constructor(map) {
+    this.map = map
+  }
+
+  updateObjectValue(obj, key, value) {
+    // XXX refactor so it's cleaner
+    let path = key.split('.')
+    let what
+    for (var i = 0, l = path.length; i < l; i++) {
+      what = path[i]
+      if (what === path[l - 1]) {
+        if (typeof value === 'undefined') {
+          delete obj[what]
+        } else {
+          obj[what] = value
+        }
+      } else {
+        obj = obj[what]
+      }
+    }
+  }
+
+  getLayerFromID(layerId) {
+    if (layerId) return this.map.getDataLayerByUmapId(layerId)
+    return this.map.defaultEditDataLayer()
+  }
+
+  applyMessage(message) {
+    let { verb } = message
+    return this[verb](message)
+  }
+}
+
+export class MapUpdater extends BaseUpdater {
+  update({ key, value }) {
+    console.log(key, value)
+    this.updateObjectValue(this.map, key, value)
+    this.map.renderProperties([key.replace('options.', '')])
+  }
+}
+
+export class DatalayerUpdater extends BaseUpdater {
+  update({ key, metadata, value }) {
+    const datalayer = this.getLayerFromID(metadata.id)
+    console.log(datalayer, key, value)
+    this.updateObjectValue(datalayer, key, value)
+    const property = key.replace('options.', '')
+    datalayer.renderProperties([property])
+  }
+}
+
+/**
+ * This is an abstract base class
+ * And needs to be subclassed to be used.
+ *
+ * The child classes need to expose:
+ * - `featureClass`: the name of the class to create the feature
+ * - `featureArgument`: an object with the properties to pass to the class when bulding it.
+ **/
+class FeatureUpdater extends BaseUpdater {
+  getFeatureFromMetadata({ id, layerId }) {
+    const datalayer = this.getLayerFromID(layerId)
+    return datalayer.getFeatureById(id)
+  }
+
+  // XXX Not sure about the naming. It's returning latlng OR latlngS
+  getGeometry({ type, coordinates }) {
+    if (type == 'Point') {
+      return L.GeoJSON.coordsToLatLng(coordinates)
+    }
+    return L.GeoJSON.coordsToLatLngs(coordinates)
+  }
+
+  upsert({ metadata, value }) {
+    let { id, layerId } = metadata
+    const datalayer = this.getLayerFromID(layerId)
+    let feature = this.getFeatureFromMetadata(metadata, value)
+    feature = datalayer.geometryToFeature({ geometry: value.geometry, id, feature })
+    feature.addTo(datalayer)
+  }
+
+  update({ key, metadata, value }) {
+    let feature = this.getFeatureFromMetadata(metadata)
+
+    switch (key) {
+      case 'geometry':
+        const datalayer = this.getLayerFromID(metadata.layerId)
+        datalayer.geometryToFeature({ geometry: value, id: metadata.id, feature })
+      default:
+        this.updateObjectValue(feature, key, value)
+    }
+
+    feature.datalayer.indexProperties(feature)
+    feature.renderProperties([key])
+  }
+
+  delete({ metadata }) {
+    // XXX Distinguish between properties getting deleted
+    // and the wole feature getting deleted
+    let feature = this.getFeatureFromMetadata(metadata)
+    if (feature) feature.del()
+  }
+}
+
+class PathUpdater extends FeatureUpdater {}
+
+class MarkerUpdater extends FeatureUpdater {
+  featureType = 'marker'
+  featureClass = U.Marker
+  featureArgument = 'latlng'
+}
+
+class PolygonUpdater extends PathUpdater {
+  featureType = 'polygon'
+  featureClass = U.Polygon
+  featureArgument = 'latlngs'
+}
+
+class PolylineUpdater extends PathUpdater {
+  featureType = 'polyline'
+  featureClass = U.Polyline
+  featureArgument = 'latlngs'
+}
+
+export { MarkerUpdater, PolygonUpdater, PolylineUpdater }
diff --git a/umap/static/umap/js/modules/sync/websocket.js b/umap/static/umap/js/modules/sync/websocket.js
new file mode 100644
index 00000000..fa103119
--- /dev/null
+++ b/umap/static/umap/js/modules/sync/websocket.js
@@ -0,0 +1,22 @@
+export class WebSocketTransport {
+  constructor(webSocketURI, authToken, messagesReceiver) {
+    this.websocket = new WebSocket(webSocketURI)
+    this.websocket.onopen = () => {
+      this.send('join', { token: authToken })
+    }
+    this.websocket.addEventListener('message', this.onMessage.bind(this))
+    this.receiver = messagesReceiver
+  }
+
+  onMessage(wsMessage) {
+    // XXX validate incoming data.
+    this.receiver.dispatch(JSON.parse(wsMessage.data))
+  }
+
+  send(kind, payload) {
+    const message = { ...payload }
+    message.kind = kind
+    let encoded = JSON.stringify(message)
+    this.websocket.send(encoded)
+  }
+}
diff --git a/umap/static/umap/js/umap.js b/umap/static/umap/js/umap.js
index c9ea9d0c..d8d6a839 100644
--- a/umap/static/umap/js/umap.js
+++ b/umap/static/umap/js/umap.js
@@ -248,6 +248,17 @@ U.Map = L.Map.extend({
     this.backup()
     this.initContextMenu()
     this.on('click contextmenu.show', this.closeInplaceToolbar)
+
+    Promise.resolve(this.getSyncEngine())
+  },
+
+  getSyncEngine: async function () {
+    // Get the authentication token from the server
+    // And pass it to the sync engine.
+    const [response, _, error] = await this.server.get('/map/2/ws-token/')
+    if (!error) {
+      this.sync = new U.SyncEngine(this, 'ws://localhost:8001', response.token)
+    }
   },
 
   render: function (fields) {