diff --git a/lodash/lodash-tests.ts b/lodash/lodash-tests.ts
index deb05249e..01aedc432 100644
--- a/lodash/lodash-tests.ts
+++ b/lodash/lodash-tests.ts
@@ -7262,6 +7262,245 @@ module TestAssignWith {
     }
 }
 
+// _.assignIn
+module TestAssignIn {
+    interface Obj {a: string};
+    interface S1 {a: number};
+    interface S2 {b: number};
+    interface S3 {c: number};
+    interface S4 {d: number};
+    interface S5 {e: number};
+
+    let obj: Obj;
+    let s1: S1;
+    let s2: S2;
+    let s3: S3;
+    let s4: S4;
+    let s5: S5;
+
+    let customizer: (objectValue: any, sourceValue: any, key?: string, object?: {}, source?: {}) => any;
+
+    {
+        let result: Obj;
+
+        result = _.assignIn<Obj>(obj);
+    }
+
+    {
+        let result: {a: number};
+
+        result = _.assignIn<Obj, S1, {a: number}>(obj, s1);
+    }
+
+    {
+        let result: {a: number, b: number};
+
+        result = _.assignIn<Obj, S1, S2, {a: number, b: number}>(obj, s1, s2);
+    }
+
+    {
+        let result: {a: number, b: number, c: number};
+
+        result = _.assignIn<Obj, S1, S2, S3, {a: number, b: number, c: number}>(obj, s1, s2, s3);
+    }
+
+    {
+        let result: {a: number, b: number, c: number, d: number};
+
+        result = _.assignIn<Obj, S1, S2, S3, S4, {a: number, b: number, c: number, d: number}>(obj, s1, s2, s3, s4);
+    }
+
+    {
+        let result: {a: number, b: number, c: number, d: number, e: number};
+
+        result = _.assignIn<Obj, {a: number, b: number, c: number, d: number, e: number}>(obj, s1, s2, s3, s4, s5);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<Obj>;
+
+        result = _(obj).assignIn();
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number}>;
+
+        result = _(obj).assignIn<S1, {a: number}>(s1);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number, b: number}>;
+
+        result = _(obj).assignIn<S1, S2, {a: number, b: number}>(s1, s2);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number, b: number, c: number}>;
+
+        result = _(obj).assignIn<S1, S2, S3, {a: number, b: number, c: number}>(s1, s2, s3);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number, b: number, c: number, d: number}>;
+
+        result = _(obj).assignIn<S1, S2, S3, S4, {a: number, b: number, c: number, d: number}>(s1, s2, s3, s4);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number, b: number, c: number, d: number, e: number}>;
+
+        result = _(obj).assignIn<{a: number, b: number, c: number, d: number, e: number}>(s1, s2, s3, s4, s5);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<Obj>;
+
+        result = _(obj).chain().assignIn();
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number}>;
+
+        result = _(obj).chain().assignIn<S1, {a: number}>(s1);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number, b: number}>;
+
+        result = _(obj).chain().assignIn<S1, S2, {a: number, b: number}>(s1, s2);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number, b: number, c: number}>;
+
+        result = _(obj).chain().assignIn<S1, S2, S3, {a: number, b: number, c: number}>(s1, s2, s3);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number, b: number, c: number, d: number}>;
+
+        result = _(obj).chain().assignIn<S1, S2, S3, S4, {a: number, b: number, c: number, d: number}>(s1, s2, s3, s4);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number, b: number, c: number, d: number, e: number}>;
+
+        result = _(obj).chain().assignIn<{a: number, b: number, c: number, d: number, e: number}>(s1, s2, s3, s4, s5);
+    }
+}
+
+// _.assignInWith
+module TestAssignInWith {
+    interface Obj {a: string};
+    interface S1 {a: number};
+    interface S2 {b: number};
+    interface S3 {c: number};
+    interface S4 {d: number};
+    interface S5 {e: number};
+
+    let obj: Obj;
+    let s1: S1;
+    let s2: S2;
+    let s3: S3;
+    let s4: S4;
+    let s5: S5;
+
+    let customizer: (objectValue: any, sourceValue: any, key?: string, object?: {}, source?: {}) => any;
+
+    {
+        let result: Obj;
+
+        result = _.assignInWith<Obj>(obj);
+    }
+
+    {
+        let result: {a: number};
+        result = _.assignInWith<Obj, S1, {a: number}>(obj, s1, customizer);
+    }
+
+    {
+        let result: {a: number, b: number};
+        result = _.assignInWith<Obj, S1, S2, {a: number, b: number}>(obj, s1, s2, customizer);
+    }
+
+    {
+        let result: {a: number, b: number, c: number};
+        result = _.assignInWith<Obj, S1, S2, S3, {a: number, b: number, c: number}>(obj, s1, s2, s3, customizer);
+    }
+
+    {
+        let result: {a: number, b: number, c: number, d: number};
+        result = _.assignInWith<Obj, S1, S2, S3, S4, {a: number, b: number, c: number, d: number}>(obj, s1, s2, s3, s4, customizer);
+    }
+
+    {
+        let result: {a: number, b: number, c: number, d: number, e: number};
+        result = _.assignInWith<Obj, {a: number, b: number, c: number, d: number, e: number}>(obj, s1, s2, s3, s4, s5, customizer);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<Obj>;
+
+        result = _(obj).assignInWith();
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number}>;
+        result = _(obj).assignInWith<S1, {a: number}>(s1, customizer);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number, b: number}>;
+        result = _(obj).assignInWith<S1, S2, {a: number, b: number}>(s1, s2, customizer);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number, b: number, c: number}>;
+        result = _(obj).assignInWith<S1, S2, S3, {a: number, b: number, c: number}>(s1, s2, s3, customizer);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number, b: number, c: number, d: number}>;
+        result = _(obj).assignInWith<S1, S2, S3, S4, {a: number, b: number, c: number, d: number}>(s1, s2, s3, s4, customizer);
+    }
+
+    {
+        let result: _.LoDashImplicitObjectWrapper<{a: number, b: number, c: number, d: number, e: number}>;
+        result = _(obj).assignInWith<{a: number, b: number, c: number, d: number, e: number}>(s1, s2, s3, s4, s5, customizer);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<Obj>;
+
+        result = _(obj).chain().assignInWith();
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number}>;
+        result = _(obj).chain().assignInWith<S1, {a: number}>(s1, customizer);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number, b: number}>;
+        result = _(obj).chain().assignInWith<S1, S2, {a: number, b: number}>(s1, s2, customizer);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number, b: number, c: number}>;
+        result = _(obj).chain().assignInWith<S1, S2, S3, {a: number, b: number, c: number}>(s1, s2, s3, customizer);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number, b: number, c: number, d: number}>;
+        result = _(obj).chain().assignInWith<S1, S2, S3, S4, {a: number, b: number, c: number, d: number}>(s1, s2, s3, s4, customizer);
+    }
+
+    {
+        let result: _.LoDashExplicitObjectWrapper<{a: number, b: number, c: number, d: number, e: number}>;
+        result = _(obj).chain().assignInWith<{a: number, b: number, c: number, d: number, e: number}>(s1, s2, s3, s4, s5, customizer);
+    }
+}
+
 // _.create
 module TestCreate {
     type SampleProto = {a: number};
diff --git a/lodash/lodash.d.ts b/lodash/lodash.d.ts
index 7c6a46754..3f596a202 100644
--- a/lodash/lodash.d.ts
+++ b/lodash/lodash.d.ts
@@ -11831,7 +11831,365 @@ declare module _ {
         assignWith<TResult extends {}>(...otherArgs: any[]): LoDashExplicitObjectWrapper<TResult>;
     }
 
+    //_.assignIn
+    interface LoDashStatic {
+        /**
+         * This method is like `_.assign` except that it iterates over own and
+         * inherited source properties.
+         *
+         * **Note:** This method mutates `object`.
+         *
+         * @static
+         * @memberOf _
+         * @alias extend
+         * @category Object
+         * @param {Object} object The destination object.
+         * @param {...Object} [sources] The source objects.
+         * @returns {Object} Returns `object`.
+         * @example
+         *
+         * function Foo() {
+         *   this.b = 2;
+         * }
+         *
+         * function Bar() {
+         *   this.d = 4;
+         * }
+         *
+         * Foo.prototype.c = 3;
+         * Bar.prototype.e = 5;
+         *
+         * _.assignIn({ 'a': 1 }, new Foo, new Bar);
+         * // => { 'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5 }
+         */
+        assignIn<TObject extends {}, TSource extends {}, TResult extends {}>(
+            object: TObject,
+            source: TSource
+        ): TResult;
 
+        /**
+         * @see assignIn
+         */
+        assignIn<TObject extends {}, TSource1 extends {}, TSource2 extends {}, TResult extends {}>(
+            object: TObject,
+            source1: TSource1,
+            source2: TSource2
+        ): TResult;
+
+        /**
+         * @see assignIn
+         */
+        assignIn<TObject extends {}, TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TResult extends {}>(
+            object: TObject,
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3
+        ): TResult;
+
+        /**
+         * @see assignIn
+         */
+        assignIn<TObject extends {}, TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TSource4 extends {},
+            TResult extends {}>
+        (
+            object: TObject,
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3,
+            source4: TSource4
+        ): TResult;
+
+        /**
+         * @see _.assignIn
+         */
+        assignIn<TObject extends {}>(object: TObject): TObject;
+
+        /**
+         * @see _.assignIn
+         */
+        assignIn<TObject extends {}, TResult extends {}>(
+            object: TObject, ...otherArgs: any[]
+        ): TResult;
+    }
+
+    interface LoDashImplicitObjectWrapper<T> {
+        /**
+         * @see _.assignIn
+         */
+        assignIn<TSource extends {}, TResult extends {}>(
+            source: TSource
+        ): LoDashImplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignIn
+         */
+        assignIn<TSource1 extends {}, TSource2 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2
+        ): LoDashImplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignIn
+         */
+        assignIn<TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3
+        ): LoDashImplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignIn
+         */
+        assignIn<TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TSource4 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3,
+            source4: TSource4
+        ): LoDashImplicitObjectWrapper<TResult>;
+
+        /**
+         * @see _.assignIn
+         */
+        assignIn(): LoDashImplicitObjectWrapper<T>;
+
+        /**
+         * @see _.assignIn
+         */
+        assignIn<TResult extends {}>(...otherArgs: any[]): LoDashImplicitObjectWrapper<TResult>;
+    }
+
+    interface LoDashExplicitObjectWrapper<T> {
+        /**
+         * @see _.assignIn
+         */
+        assignIn<TSource extends {}, TResult extends {}>(
+            source: TSource
+        ): LoDashExplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignIn
+         */
+        assignIn<TSource1 extends {}, TSource2 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2
+        ): LoDashExplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignIn
+         */
+        assignIn<TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3
+        ): LoDashExplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignIn
+         */
+        assignIn<TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TSource4 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3,
+            source4: TSource4
+        ): LoDashExplicitObjectWrapper<TResult>;
+
+        /**
+         * @see _.assignIn
+         */
+        assignIn(): LoDashExplicitObjectWrapper<T>;
+
+        /**
+         * @see _.assignIn
+         */
+        assignIn<TResult extends {}>(...otherArgs: any[]): LoDashExplicitObjectWrapper<TResult>;
+    }
+
+    //_.assignInWith
+    interface AssignCustomizer {
+        (objectValue: any, sourceValue: any, key?: string, object?: {}, source?: {}): any;
+    }
+
+    interface LoDashStatic {
+        /**
+         * This method is like `_.assignIn` except that it accepts `customizer` which
+         * is invoked to produce the assigned values. If `customizer` returns `undefined`
+         * assignment is handled by the method instead. The `customizer` is invoked
+         * with five arguments: (objValue, srcValue, key, object, source).
+         *
+         * **Note:** This method mutates `object`.
+         *
+         * @static
+         * @memberOf _
+         * @alias extendWith
+         * @category Object
+         * @param {Object} object The destination object.
+         * @param {...Object} sources The source objects.
+         * @param {Function} [customizer] The function to customize assigned values.
+         * @returns {Object} Returns `object`.
+         * @example
+         *
+         * function customizer(objValue, srcValue) {
+         *   return _.isUndefined(objValue) ? srcValue : objValue;
+         * }
+         *
+         * var defaults = _.partialRight(_.assignInWith, customizer);
+         *
+         * defaults({ 'a': 1 }, { 'b': 2 }, { 'a': 3 });
+         * // => { 'a': 1, 'b': 2 }
+         */
+        assignInWith<TObject extends {}, TSource extends {}, TResult extends {}>(
+            object: TObject,
+            source: TSource,
+            customizer: AssignCustomizer
+        ): TResult;
+
+        /**
+         * @see assignInWith
+         */
+        assignInWith<TObject extends {}, TSource1 extends {}, TSource2 extends {}, TResult extends {}>(
+            object: TObject,
+            source1: TSource1,
+            source2: TSource2,
+            customizer: AssignCustomizer
+        ): TResult;
+
+        /**
+         * @see assignInWith
+         */
+        assignInWith<TObject extends {}, TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TResult extends {}>(
+            object: TObject,
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3,
+            customizer: AssignCustomizer
+        ): TResult;
+
+        /**
+         * @see assignInWith
+         */
+        assignInWith<TObject extends {}, TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TSource4 extends {},
+            TResult extends {}>
+        (
+            object: TObject,
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3,
+            source4: TSource4,
+            customizer: AssignCustomizer
+        ): TResult;
+
+        /**
+         * @see _.assignInWith
+         */
+        assignInWith<TObject extends {}>(object: TObject): TObject;
+
+        /**
+         * @see _.assignInWith
+         */
+        assignInWith<TObject extends {}, TResult extends {}>(
+            object: TObject, ...otherArgs: any[]
+        ): TResult;
+    }
+
+    interface LoDashImplicitObjectWrapper<T> {
+        /**
+         * @see _.assignInWith
+         */
+        assignInWith<TSource extends {}, TResult extends {}>(
+            source: TSource,
+            customizer: AssignCustomizer
+        ): LoDashImplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignInWith
+         */
+        assignInWith<TSource1 extends {}, TSource2 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            customizer: AssignCustomizer
+        ): LoDashImplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignInWith
+         */
+        assignInWith<TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3,
+            customizer: AssignCustomizer
+        ): LoDashImplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignInWith
+         */
+        assignInWith<TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TSource4 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3,
+            source4: TSource4,
+            customizer: AssignCustomizer
+        ): LoDashImplicitObjectWrapper<TResult>;
+
+        /**
+         * @see _.assignInWith
+         */
+        assignInWith(): LoDashImplicitObjectWrapper<T>;
+
+        /**
+         * @see _.assignInWith
+         */
+        assignInWith<TResult extends {}>(...otherArgs: any[]): LoDashImplicitObjectWrapper<TResult>;
+    }
+
+    interface LoDashExplicitObjectWrapper<T> {
+        /**
+         * @see _.assignInWith
+         */
+        assignInWith<TSource extends {}, TResult extends {}>(
+            source: TSource,
+            customizer: AssignCustomizer
+        ): LoDashExplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignInWith
+         */
+        assignInWith<TSource1 extends {}, TSource2 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            customizer: AssignCustomizer
+        ): LoDashExplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignInWith
+         */
+        assignInWith<TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3,
+            customizer: AssignCustomizer
+        ): LoDashExplicitObjectWrapper<TResult>;
+
+        /**
+         * @see assignInWith
+         */
+        assignInWith<TSource1 extends {}, TSource2 extends {}, TSource3 extends {}, TSource4 extends {}, TResult extends {}>(
+            source1: TSource1,
+            source2: TSource2,
+            source3: TSource3,
+            source4: TSource4,
+            customizer: AssignCustomizer
+        ): LoDashExplicitObjectWrapper<TResult>;
+
+        /**
+         * @see _.assignInWith
+         */
+        assignInWith(): LoDashExplicitObjectWrapper<T>;
+
+        /**
+         * @see _.assignInWith
+         */
+        assignInWith<TResult extends {}>(...otherArgs: any[]): LoDashExplicitObjectWrapper<TResult>;
+    }
 
     //_.create
     interface LoDashStatic {