diff --git a/src/index.ts b/src/index.ts
index e06a4e3c..1e54f412 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -23,19 +23,7 @@ import {
   processNonStream,
   processStream,
 } from './process_stream';
-import {
-  Content,
-  CountTokensRequest,
-  CountTokensResponse,
-  GenerateContentRequest,
-  GenerateContentResult,
-  GenerationConfig,
-  ModelParams,
-  Part,
-  SafetySetting,
-  StreamGenerateContentResult,
-  VertexInit,
-} from './types/content';
+import {Content, CountTokensRequest, CountTokensResponse, GenerateContentRequest, GenerateContentResult, GenerationConfig, ModelParams, Part, SafetySetting, StreamGenerateContentResult, Tool, VertexInit,} from './types/content';
 import {
   ClientError,
   GoogleAuthError,
@@ -126,11 +114,8 @@ export class VertexAI_Preview {
     }
 
     return new GenerativeModel(
-      this,
-      modelParams.model,
-      modelParams.generation_config,
-      modelParams.safety_settings
-    );
+        this, modelParams.model, modelParams.generation_config,
+        modelParams.safety_settings, modelParams.tools);
   }
 }
 
@@ -141,6 +126,7 @@ export declare interface StartChatParams {
   history?: Content[];
   safety_settings?: SafetySetting[];
   generation_config?: GenerationConfig;
+  tools?: Tool[];
   stream?: boolean;
 }
 
@@ -174,6 +160,7 @@ export class ChatSession {
   private _send_stream_promise: Promise<void> = Promise.resolve();
   generation_config?: GenerationConfig;
   safety_settings?: SafetySetting[];
+  tools?: Tool[];
 
   get history(): Content[] {
     return this.historyInternal;
@@ -200,6 +187,7 @@ export class ChatSession {
       contents: this.historyInternal.concat([newContent]),
       safety_settings: this.safety_settings,
       generation_config: this.generation_config,
+      tools: this.tools,
     };
 
     const generateContentResult: GenerateContentResult =
@@ -262,6 +250,7 @@ export class ChatSession {
       contents: this.historyInternal.concat([newContent]),
       safety_settings: this.safety_settings,
       generation_config: this.generation_config,
+      tools: this.tools,
     };
 
     const streamGenerateContentResultPromise = this._model_instance
@@ -289,6 +278,7 @@ export class GenerativeModel {
   model: string;
   generation_config?: GenerationConfig;
   safety_settings?: SafetySetting[];
+  tools?: Tool[];
   private _vertex_instance: VertexAI_Preview;
   private _use_non_stream = false;
   private publisherModelEndpoint: string;
@@ -302,15 +292,14 @@ export class GenerativeModel {
    * @param {SafetySetting[]} safety_settings - Optional. {@link SafetySetting}
    */
   constructor(
-    vertex_instance: VertexAI_Preview,
-    model: string,
-    generation_config?: GenerationConfig,
-    safety_settings?: SafetySetting[]
-  ) {
+      vertex_instance: VertexAI_Preview, model: string,
+      generation_config?: GenerationConfig, safety_settings?: SafetySetting[],
+      tools?: Tool[]) {
     this._vertex_instance = vertex_instance;
     this.model = model;
     this.generation_config = generation_config;
     this.safety_settings = safety_settings;
+    this.tools = tools;
     if (model.startsWith('models/')) {
       this.publisherModelEndpoint = `publishers/google/${this.model}`;
     } else {
@@ -349,6 +338,7 @@ export class GenerativeModel {
       contents: request.contents,
       generation_config: request.generation_config ?? this.generation_config,
       safety_settings: request.safety_settings ?? this.safety_settings,
+      tools: request.tools ?? [],
     };
 
     const response: Response | undefined = await postRequest({
@@ -387,6 +377,7 @@ export class GenerativeModel {
       contents: request.contents,
       generation_config: request.generation_config ?? this.generation_config,
       safety_settings: request.safety_settings ?? this.safety_settings,
+      tools: request.tools ?? [],
     };
     const response = await postRequest({
       region: this._vertex_instance.location,
@@ -444,6 +435,7 @@ export class GenerativeModel {
         request.generation_config ?? this.generation_config;
       startChatRequest.safety_settings =
         request.safety_settings ?? this.safety_settings;
+      startChatRequest.tools = request.tools ?? this.tools;
     }
     return new ChatSession(startChatRequest);
   }
@@ -464,7 +456,16 @@ function formulateNewContent(request: string | Array<string | Part>): Content {
     }
   }
 
-  const newContent: Content = {role: constants.USER_ROLE, parts: newParts};
+  let newContent = {} as Content;
+
+  // TODO: this assumes all elements of newParts are of the same Part type
+  if ('functionResponse' in newParts[0]) {
+    newContent.role = constants.FUNCTION_ROLE;
+  } else {
+    newContent.role = constants.USER_ROLE;
+  }
+
+  newContent.parts = newParts;
   return newContent;
 }
 
diff --git a/src/process_stream.ts b/src/process_stream.ts
index 1e62cf78..a762bfdd 100644
--- a/src/process_stream.ts
+++ b/src/process_stream.ts
@@ -193,6 +193,10 @@ function aggregateResponses(
           if (part.text) {
             aggregatedResponse.candidates[i].content.parts[0].text += part.text;
           }
+          if (part.functionCall) {
+            aggregatedResponse.candidates[i].content.parts[0].functionCall =
+                part.functionCall;
+          }
         }
       }
     }
diff --git a/src/types/content.ts b/src/types/content.ts
index 6adb61c2..18d5c659 100644
--- a/src/types/content.ts
+++ b/src/types/content.ts
@@ -64,6 +64,7 @@ export declare interface ModelParams extends BaseModelParams {
 export declare interface BaseModelParams {
   safety_settings?: SafetySetting[];
   generation_config?: GenerationConfig;
+  tools?: Tool[];
 }
 
 /**
@@ -156,24 +157,38 @@ export interface BasePart {}
 export interface TextPart extends BasePart {
   text: string;
   inline_data?: never;
+  functionResponse?: never;
+  functionCall?: never;
 }
 
 export interface InlineDataPart extends BasePart {
   text?: never;
   inline_data: GenerativeContentBlob;
+  functionResponse?: never;
+  functionCall?: never;
 }
 
 export interface FileData {
   mime_type: string;
   file_uri: string;
+  functionCall?: never;
 }
 
 export interface FileDataPart extends BasePart {
   text?: never;
   file_data: FileData;
+  functionResponse?: never;
+  functionCall?: never;
 }
 
-export declare type Part = TextPart | InlineDataPart | FileDataPart;
+export interface FunctionResponsePart extends BasePart {
+  text?: never;
+  functionResponse?: FunctionResponse;
+  functionCall?: FunctionCall;
+}
+
+export declare type Part =
+    TextPart | InlineDataPart | FileDataPart | FunctionResponsePart;
 
 /**
  * Raw media bytes sent directly in the request. Text should not be sent as
@@ -269,6 +284,12 @@ export declare interface GenerateContentCandidate {
   finishMessage?: string;
   safetyRatings?: SafetyRating[];
   citationMetadata?: CitationMetadata;
+  functionCall?: FunctionCall;
+}
+
+export declare interface FunctionCall {
+  name: string;
+  args: object;
 }
 
 /**
@@ -287,3 +308,22 @@ export declare interface CitationSource {
   uri?: string;
   license?: string;
 }
+
+export declare interface FunctionResponse {
+  name: string;
+  response: object;
+}
+
+export declare interface FunctionParameters {
+  properties: object;
+}
+
+export declare interface FunctionDeclaration {
+  name: string;
+  parameters: FunctionParameters;
+  description?: string;
+}
+
+export declare interface Tool {
+  function_declarations: FunctionDeclaration[];
+}
\ No newline at end of file
diff --git a/src/util/constants.ts b/src/util/constants.ts
index 9bff4fa1..4fae89e2 100644
--- a/src/util/constants.ts
+++ b/src/util/constants.ts
@@ -18,6 +18,7 @@ export const GENERATE_CONTENT_METHOD = 'generateContent';
 export const STREAMING_GENERATE_CONTENT_METHOD = 'streamGenerateContent';
 export const USER_ROLE = 'user';
 export const MODEL_ROLE = 'model';
+export const FUNCTION_ROLE = 'function';
 const USER_AGENT_PRODUCT = 'model-builder';
 const CLIENT_LIBRARY_LANGUAGE = 'grpc-node/18.0.0';
 const CLIENT_LIBRARY_VERSION = '0.1.3';