diff --git a/packages/firestore/src/model/document.ts b/packages/firestore/src/model/document.ts
index 747f8bf49ef..5fe125d0eaa 100644
--- a/packages/firestore/src/model/document.ts
+++ b/packages/firestore/src/model/document.ts
@@ -93,7 +93,9 @@ export class Document extends MaybeDocument {
 
   toString(): string {
     return (
-      `Document(${this.key}, ${this.version}, ${this.objectValue.toString()}, ` +
+      `Document(${this.key}, ${
+        this.version
+      }, ${this.objectValue.toString()}, ` +
       `{hasLocalMutations: ${this.hasLocalMutations}}), ` +
       `{hasCommittedMutations: ${this.hasCommittedMutations}})`
     );
diff --git a/packages/firestore/src/model/proto_values.ts b/packages/firestore/src/model/proto_values.ts
index 7d0d381deeb..89db3a32883 100644
--- a/packages/firestore/src/model/proto_values.ts
+++ b/packages/firestore/src/model/proto_values.ts
@@ -335,6 +335,88 @@ function compareMaps(left: api.MapValue, right: api.MapValue): number {
   return primitiveComparator(leftKeys.length, rightKeys.length);
 }
 
+/**
+ * Generates the canonical ID for the provided field value (as used in Target
+ * serialization).
+ */
+export function canonicalId(value: api.Value): string {
+  return canonifyValue(value);
+}
+
+function canonifyValue(value: api.Value): string {
+  if ('nullValue' in value) {
+    return 'null';
+  } else if ('booleanValue' in value) {
+    return '' + value.booleanValue!;
+  } else if ('integerValue' in value) {
+    return '' + value.integerValue!;
+  } else if ('doubleValue' in value) {
+    return '' + value.doubleValue!;
+  } else if ('timestampValue' in value) {
+    return canonifyTimestamp(value.timestampValue!);
+  } else if ('stringValue' in value) {
+    return value.stringValue!;
+  } else if ('bytesValue' in value) {
+    return canonifyByteString(value.bytesValue!);
+  } else if ('referenceValue' in value) {
+    // TODO(mrschmidt): Use document key only
+    return value.referenceValue!;
+  } else if ('geoPointValue' in value) {
+    return canonifyGeoPoint(value.geoPointValue!);
+  } else if ('arrayValue' in value) {
+    return canonifyArray(value.arrayValue!);
+  } else if ('mapValue' in value) {
+    return canonifyMap(value.mapValue!);
+  } else {
+    return fail('Invalid value type: ' + JSON.stringify(value));
+  }
+}
+
+function canonifyByteString(byteString: string | Uint8Array): string {
+  return normalizeByteString(byteString).toBase64();
+}
+
+function canonifyTimestamp(timestamp: ProtoTimestampValue): string {
+  const normalizedTimestamp = normalizeTimestamp(timestamp);
+  return `time(${normalizedTimestamp.seconds},${normalizedTimestamp.nanos})`;
+}
+
+function canonifyGeoPoint(geoPoint: api.LatLng): string {
+  return `geo(${geoPoint.latitude},${geoPoint.longitude})`;
+}
+
+function canonifyMap(mapValue: api.MapValue): string {
+  // Iteration order in JavaScript is not guaranteed. To ensure that we generate
+  // matching canonical IDs for identical maps, we need to sort the keys.
+  const sortedKeys = keys(mapValue.fields || {}).sort();
+
+  let result = '{';
+  let first = true;
+  for (const key of sortedKeys) {
+    if (!first) {
+      result += ',';
+    } else {
+      first = false;
+    }
+    result += `${key}:${canonifyValue(mapValue.fields![key])}`;
+  }
+  return result + '}';
+}
+
+function canonifyArray(arrayValue: api.ArrayValue): string {
+  let result = '[';
+  let first = true;
+  for (const value of arrayValue.values || []) {
+    if (!first) {
+      result += ',';
+    } else {
+      first = false;
+    }
+    result += canonifyValue(value);
+  }
+  return result + ']';
+}
+
 /**
  * Converts the possible Proto values for a timestamp value into a "seconds and
  * nanos" representation.
diff --git a/packages/firestore/test/unit/model/field_value.test.ts b/packages/firestore/test/unit/model/field_value.test.ts
index b11f702cb88..2818b35bf44 100644
--- a/packages/firestore/test/unit/model/field_value.test.ts
+++ b/packages/firestore/test/unit/model/field_value.test.ts
@@ -29,6 +29,7 @@ import {
   ObjectValue,
   PrimitiveValue
 } from '../../../src/model/proto_field_value';
+import { canonicalId } from '../../../src/model/proto_values';
 import { ByteString } from '../../../src/util/byte_string';
 import { primitiveComparator } from '../../../src/util/misc';
 import * as typeUtils from '../../../src/util/types';
@@ -720,6 +721,59 @@ describe('FieldValue', () => {
     }
   });
 
+  it('canonicalizes values', () => {
+    expect(canonicalId(wrap(null).proto)).to.equal('null');
+    expect(canonicalId(wrap(true).proto)).to.equal('true');
+    expect(canonicalId(wrap(false).proto)).to.equal('false');
+    expect(canonicalId(wrap(1).proto)).to.equal('1');
+    expect(canonicalId(wrap(1.1).proto)).to.equal('1.1');
+    expect(canonicalId(wrap(new Timestamp(30, 60)).proto)).to.equal(
+      'time(30,60)'
+    );
+    expect(canonicalId(wrap('a').proto)).to.equal('a');
+    expect(canonicalId(wrap(blob(1, 2, 3)).proto)).to.equal('AQID');
+    expect(
+      canonicalId(wrapRef(dbId('p1', 'd1'), key('c1/doc1')).proto)
+    ).to.equal('projects/p1/databases/d1/documents/c1/doc1');
+    expect(canonicalId(wrap(new GeoPoint(30, 60)).proto)).to.equal(
+      'geo(30,60)'
+    );
+    expect(canonicalId(wrap([1, 2, 3]).proto)).to.equal('[1,2,3]');
+    expect(
+      canonicalId(
+        wrap({
+          'a': 1,
+          'b': 2,
+          'c': '3'
+        }).proto
+      )
+    ).to.equal('{a:1,b:2,c:3}');
+    expect(
+      canonicalId(wrap({ 'a': ['b', { 'c': new GeoPoint(30, 60) }] }).proto)
+    ).to.equal('{a:[b,{c:geo(30,60)}]}');
+  });
+
+  it('canonical IDs ignore sort order', () => {
+    expect(
+      canonicalId(
+        wrap({
+          'a': 1,
+          'b': 2,
+          'c': '3'
+        }).proto
+      )
+    ).to.equal('{a:1,b:2,c:3}');
+    expect(
+      canonicalId(
+        wrap({
+          'c': 3,
+          'b': 2,
+          'a': '1'
+        }).proto
+      )
+    ).to.equal('{a:1,b:2,c:3}');
+  });
+
   function setField(
     objectValue: ObjectValue,
     fieldPath: string,