diff --git a/src/utils/IdMap.js b/src/utils/IdMap.js
index d91f9e02..8459a6ee 100644
--- a/src/utils/IdMap.js
+++ b/src/utils/IdMap.js
@@ -1,12 +1,13 @@
 import {
   _diffSet,
   findIndexInIdRanges,
-  IdSet, ID // eslint-disable-line
+  DSDecoderV1, DSDecoderV2,  DSEncoderV1, DSEncoderV2, IdSet, ID // eslint-disable-line
 } from '../internals.js'
 
 import * as array from 'lib0/array'
 import * as map from 'lib0/map'
 import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
 import * as buf from 'lib0/buffer'
 import * as rabin from 'lib0/hash/rabin'
 
@@ -41,7 +42,6 @@ const _hashAttribution = attr => {
   return buf.toBase64(rabin.fingerprint(rabin.StandardIrreducible128, encoding.toUint8Array(encoder)))
 }
 
-
 /**
  * @template V
  * @param {string} name
@@ -126,6 +126,7 @@ export class AttrRanges {
    * @param {Array<Attribution<Attrs>>} attrs
    */
   add (clock, length, attrs) {
+    if (length === 0) return
     this.sorted = false
     this._ids.push(new AttrRange(clock, length, attrs))
   }
@@ -325,6 +326,7 @@ export class IdMap {
    * @param {Array<Attribution<Attrs>>} attrs
    */
   add (client, clock, len, attrs) {
+    if (len === 0) return
     attrs = _ensureAttrs(this, attrs)
     const ranges = this.clients.get(client)
     if (ranges == null) {
@@ -335,6 +337,146 @@ export class IdMap {
   }
 }
 
+/**
+ * Efficiently encodes IdMap to a binary form. Ensures that information is de-duplicated when
+ * written. Attribute.names are referenced by id. Attributes themselfs are also referenced by id.
+ *
+ * @template Attr
+ * @param {DSEncoderV1 | DSEncoderV2} encoder
+ * @param {IdMap<Attr>} idmap
+ *
+ * @private
+ * @function
+ */
+export const writeIdMap = (encoder, idmap) => {
+  encoding.writeVarUint(encoder.restEncoder, idmap.clients.size)
+  let lastWrittenClientId = 0
+  /**
+   * @type {Map<Attribution<Attr>, number>}
+   */
+  const visitedAttributions = map.create()
+  /**
+   * @type {Map<string, number>}
+   */
+  const visitedAttrNames = map.create()
+  // Ensure that the delete set is written in a deterministic order (smaller clientids first)
+  array.from(idmap.clients.entries())
+    .sort((a, b) => a[0] - b[0])
+    .forEach(([client, _idRanges]) => {
+      const attrRanges = _idRanges.getIds()
+      encoder.resetDsCurVal()
+      const diff = client - lastWrittenClientId
+      encoding.writeVarUint(encoder.restEncoder, diff)
+      lastWrittenClientId = client
+      const len = attrRanges.length
+      encoding.writeVarUint(encoder.restEncoder, len)
+      for (let i = 0; i < len; i++) {
+        const item = attrRanges[i]
+        const attrs = item.attrs
+        const attrLen = attrs.length
+        encoder.writeDsClock(item.clock)
+        encoder.writeDsLen(item.len)
+        encoding.writeVarUint(encoder.restEncoder, attrLen)
+        for (let j = 0; j < attrLen; j++) {
+          const attr = attrs[j]
+          const attrId = visitedAttributions.get(attr)
+          if (attrId != null) {
+            encoding.writeVarUint(encoder.restEncoder, attrId)
+          } else {
+            const newAttrId = visitedAttributions.size
+            visitedAttributions.set(attr, newAttrId)
+            encoding.writeVarUint(encoder.restEncoder, newAttrId)
+            const attrNameId = visitedAttrNames.get(attr.name)
+            // write attr.name
+            if (attrNameId != null) {
+              encoding.writeVarUint(encoder.restEncoder, attrNameId)
+            } else {
+              const newAttrNameId = visitedAttrNames.size
+              encoding.writeVarUint(encoder.restEncoder, newAttrNameId)
+              encoding.writeVarString(encoder.restEncoder, attr.name)
+              visitedAttrNames.set(attr.name, newAttrNameId)
+            }
+            encoding.writeAny(encoder.restEncoder, /** @type {any} */ (attr.val))
+          }
+        }
+      }
+    })
+}
+
+/**
+ * @param {IdMap<any>} idmap
+ */
+export const encodeIdMap = idmap => {
+  const encoder = new DSEncoderV2()
+  writeIdMap(encoder, idmap)
+  return encoder.toUint8Array()
+}
+
+/**
+ * @param {DSDecoderV1 | DSDecoderV2} decoder
+ * @return {IdMap<any>}
+ *
+ * @private
+ * @function
+ */
+export const readIdMap = decoder => {
+  const idmap = new IdMap()
+  const numClients = decoding.readVarUint(decoder.restDecoder)
+  /**
+   * @type {Array<Attribution<any>>}
+   */
+  const visitedAttributions = []
+  /**
+   * @type {Array<string>}
+   */
+  const visitedAttrNames = []
+  let lastClientId = 0
+  for (let i = 0; i < numClients; i++) {
+    decoder.resetDsCurVal()
+    const client = lastClientId + decoding.readVarUint(decoder.restDecoder)
+    lastClientId = client
+    const numberOfDeletes = decoding.readVarUint(decoder.restDecoder)
+    /**
+     * @type {Array<AttrRange<any>>}
+     */
+    const attrRanges = []
+    for (let i = 0; i < numberOfDeletes; i++) {
+      const rangeClock = decoder.readDsClock()
+      const rangeLen = decoder.readDsLen()
+      /**
+       * @type {Array<Attribution<any>>}
+       */
+      const attrs = []
+      const attrsLen = decoding.readVarUint(decoder.restDecoder)
+      for (let j = 0; j < attrsLen; j++) {
+        const attrId = decoding.readVarUint(decoder.restDecoder)
+        if (attrId >= visitedAttributions.length) {
+          // attrId not known yet
+          const attrNameId = decoding.readVarUint(decoder.restDecoder)
+          if (attrNameId >= visitedAttrNames.length) {
+            visitedAttrNames.push(decoding.readVarString(decoder.restDecoder))
+          }
+          visitedAttributions.push(new Attribution(visitedAttrNames[attrNameId], decoding.readAny(decoder.restDecoder)))
+        }
+        attrs.push(visitedAttributions[attrId])
+      }
+      attrRanges.push(new AttrRange(rangeClock, rangeLen, attrs))
+    }
+    idmap.clients.set(client, new AttrRanges(attrRanges))
+  }
+  visitedAttributions.forEach(attr => {
+    idmap.attrs.add(attr)
+    idmap.attrsH.set(attr.hash(), attr)
+  })
+  return idmap
+}
+
+/**
+ * @param {Uint8Array} data
+ * @return {IdMap<any>}
+ */
+export const decodeIdMap = data => readIdMap(new DSDecoderV2(decoding.createDecoder(data)))
+
 /**
  * @template Attrs
  * @param {IdMap<Attrs>} idmap
@@ -342,10 +484,12 @@ export class IdMap {
  * @return {Array<Attribution<Attrs>>}
  */
 const _ensureAttrs = (idmap, attrs) => attrs.map(attr =>
-  idmap.attrs.has(attr) ? attr : map.setIfUndefined(idmap.attrsH, _hashAttribution(attr), () => {
-    idmap.attrs.add(attr)
-    return attr
-  }))
+  idmap.attrs.has(attr)
+    ? attr
+    : map.setIfUndefined(idmap.attrsH, _hashAttribution(attr), () => {
+      idmap.attrs.add(attr)
+      return attr
+    }))
 
 export const createIdMap = () => new IdMap()
 
@@ -358,4 +502,9 @@ export const createIdMap = () => new IdMap()
  * @param {IdSet | IdMap<any>} exclude
  * @return {ISet}
  */
-export const diffIdMap = _diffSet
+export const diffIdMap = (set, exclude) => {
+  const diffed = _diffSet(set, exclude)
+  diffed.attrs = set.attrs
+  diffed.attrsH = set.attrsH
+  return diffed
+}
diff --git a/src/utils/IdSet.js b/src/utils/IdSet.js
index 21efe141..b17a0f6a 100644
--- a/src/utils/IdSet.js
+++ b/src/utils/IdSet.js
@@ -303,6 +303,7 @@ export const diffIdSet = _diffSet
  * @function
  */
 export const addToIdSet = (idSet, client, clock, length) => {
+  if (length === 0) return
   const idRanges = idSet.clients.get(client)
   if (idRanges) {
     idRanges.add(clock, length)
diff --git a/tests/IdMap.tests.js b/tests/IdMap.tests.js
index 24388e32..b8c7578d 100644
--- a/tests/IdMap.tests.js
+++ b/tests/IdMap.tests.js
@@ -1,6 +1,7 @@
 import * as t from 'lib0/testing'
 import * as am from '../src/utils/IdMap.js'
 import { compareIdmaps, createIdMap, ID, createRandomIdSet, createRandomIdMap, createAttribution } from './testHelper.js'
+import * as YY from '../src/internals.js'
 
 /**
  * @template T
@@ -115,6 +116,8 @@ export const testRepeatRandomDiffing = tc => {
   const e1 = am.diffIdMap(ds1, ds2)
   const e2 = am.diffIdMap(merged, ds2)
   compareIdmaps(e1, e2)
+  const copy = YY.decodeIdMap(YY.encodeIdMap(e1))
+  compareIdmaps(e1, copy)
 }
 
 /**
@@ -133,4 +136,6 @@ export const testRepeatRandomDiffing2 = tc => {
   const e2 = am.diffIdMap(am2, idsExclude)
   const excludedMerged = am.mergeIdMaps([e1, e2])
   compareIdmaps(mergedExcluded, excludedMerged)
+  const copy = YY.decodeIdMap(YY.encodeIdMap(mergedExcluded))
+  compareIdmaps(mergedExcluded, copy)
 }
diff --git a/tests/testHelper.js b/tests/testHelper.js
index 6e55c746..9be857ea 100644
--- a/tests/testHelper.js
+++ b/tests/testHelper.js
@@ -8,7 +8,7 @@ import * as map from 'lib0/map'
 import * as Y from '../src/index.js'
 import * as math from 'lib0/math'
 import {
-  createIdSet, createIdMap, addToIdSet
+  createIdSet, createIdMap, addToIdSet, encodeIdMap
 } from '../src/internals.js'
 
 export * from '../src/index.js'
@@ -313,7 +313,7 @@ export const init = (tc, { users = 5 } = {}, initTestObject) => {
  * @param {Y.IdSet} idSet2
  */
 export const compareIdSets = (idSet1, idSet2) => {
-  if (idSet1.clients.size !== idSet2.clients.size) return false
+  t.assert(idSet1.clients.size === idSet2.clients.size)
   for (const [client, _items1] of idSet1.clients.entries()) {
     const items1 = _items1.getIds()
     const items2 = idSet2.clients.get(client)?.getIds()
@@ -349,13 +349,34 @@ const _idmapAttrsHas = (attrs, attr) => {
  */
 export const _idmapAttrsEqual = (a, b) => a.length === b.length && a.every(v => _idmapAttrsHas(b, v))
 
+/**
+ * Ensure that all attributes exist. Also create a copy and compare it to the original.
+ *
+ * @template T
+ * @param {Y.IdMap<T>} idmap
+ */
+export const validateIdMap = idmap => {
+  const copy = Y.createIdMap()
+  idmap.clients.forEach((ranges, client) => {
+    ranges.getIds().forEach(range => {
+      range.attrs.forEach(attr => {
+        t.assert(idmap.attrs.has(attr))
+        t.assert(idmap.attrsH.get(attr.hash()) === attr)
+        copy.add(client, range.clock, range.len, range.attrs.slice())
+      })
+    })
+    t.assert(copy.clients.get(client)?.getIds().length === ranges.getIds().length)
+  })
+  t.assert(idmap.attrsH.size === idmap.attrs.size)
+}
+
 /**
  * @template T
  * @param {Y.IdMap<T>} am1
  * @param {Y.IdMap<T>} am2
  */
 export const compareIdmaps = (am1, am2) => {
-  if (am1.clients.size !== am2.clients.size) return false
+  t.assert(am1.clients.size === am2.clients.size)
   for (const [client, _items1] of am1.clients.entries()) {
     const items1 = _items1.getIds()
     const items2 = am2.clients.get(client)?.getIds()
@@ -366,7 +387,8 @@ export const compareIdmaps = (am1, am2) => {
       t.assert(di1.clock === di2.clock && di1.len === di2.len && _idmapAttrsEqual(di1.attrs, di2.attrs))
     }
   }
-  return true
+  validateIdMap(am1)
+  validateIdMap(am2)
 }
 
 /**
@@ -416,6 +438,7 @@ export const createRandomIdMap = (gen, clients, clockRange, attrChoices) => {
     }
     idMap.add(client, clockStart, len, attrs.map(v => Y.createAttribution('', v)))
   }
+  t.info(`Created IdMap with ${numOfOps} ranges and ${attrChoices.length} different attributes. Encoded size: ${encodeIdMap(idMap).byteLength}`)
   return idMap
 }