diff --git a/README.md b/README.md
index fc60fb70..0d857527 100644
--- a/README.md
+++ b/README.md
@@ -125,6 +125,37 @@ public class Example {
 }
 ```
 
+### With Custom Thread Pool Size
+
+```java
+import com.sendgrid.*;
+import java.io.IOException;
+
+public class Example {
+  public static void main(String[] args) throws IOException {
+    Email from = new Email("test@example.com");
+    String subject = "Sending with Twilio SendGrid is Fun";
+    Email to = new Email("test@example.com");
+    Content content = new Content("text/plain", "and easy to do anywhere, even with Java");
+    Mail mail = new Mail(from, subject, to, content);
+
+    SendGrid sg = new SendGrid(System.getenv("SENDGRID_API_KEY"), 4);
+    Request request = new Request();
+    try {
+      request.setMethod(Method.POST);
+      request.setEndpoint("mail/send");
+      request.setBody(mail.build());
+      Response response = sg.api(request);
+      System.out.println(response.getStatusCode());
+      System.out.println(response.getBody());
+      System.out.println(response.getHeaders());
+    } catch (IOException ex) {
+      throw ex;
+    }
+  }
+}
+```
+
 The `Mail` constructor creates a [personalization object](https://sendgrid.com/docs/Classroom/Send/v3_Mail_Send/personalizations.html) for you. [Here](examples/helpers/mail/Example.java#L221) is an example of how to add to it.
 
 ### Without Mail Helper Class
diff --git a/src/main/java/com/sendgrid/BaseInterface.java b/src/main/java/com/sendgrid/BaseInterface.java
index 0a812c19..82771742 100644
--- a/src/main/java/com/sendgrid/BaseInterface.java
+++ b/src/main/java/com/sendgrid/BaseInterface.java
@@ -15,7 +15,7 @@ public abstract class BaseInterface implements SendGridAPI {
 
   private static final String USER_AGENT = "sendgrid/" + VERSION + ";java";
   private static final int RATE_LIMIT_RESPONSE_CODE = 429;
-  private static final int THREAD_POOL_SIZE = 8;
+  private static final int DEFAULT_THREAD_POOL_SIZE = 8;
 
   private ExecutorService pool;
 
@@ -86,6 +86,17 @@ public BaseInterface(final Client client) {
    * @param host the base URL for the API
    */
   public void initialize(final String auth, final String host) {
+    initialize(auth, host, DEFAULT_THREAD_POOL_SIZE);
+  }
+
+  /**
+   * Initialize the client.
+   *
+   * @param auth           authorization header value
+   * @param host           the base URL for the API
+   * @param threadPoolSize the pool size to initialize for sending email asynchronously
+   */
+  public void initialize(final String auth, final String host, int threadPoolSize) {
     this.host = host;
     this.version = "v3";
     this.requestHeaders = new HashMap<>();
@@ -95,7 +106,7 @@ public void initialize(final String auth, final String host) {
     this.rateLimitRetry = 5;
     this.rateLimitSleep = 1100;
 
-    this.pool = Executors.newFixedThreadPool(THREAD_POOL_SIZE);
+    this.pool = Executors.newFixedThreadPool(threadPoolSize);
   }
 
   /**
diff --git a/src/main/java/com/sendgrid/SendGrid.java b/src/main/java/com/sendgrid/SendGrid.java
index e30a00f2..a0aca306 100644
--- a/src/main/java/com/sendgrid/SendGrid.java
+++ b/src/main/java/com/sendgrid/SendGrid.java
@@ -5,6 +5,9 @@
  */
 public class SendGrid extends BaseInterface {
 
+  private static final String SENDGRID_HOST_NAME = "api.sendgrid.com";
+  public static final String BEARER = "Bearer ";
+
   /**
    * Construct a new Twilio SendGrid API wrapper.
    *
@@ -14,6 +17,16 @@ public SendGrid(final String apiKey) {
     initializeSendGrid(apiKey);
   }
 
+  /**
+   * Construct a new Twilio SendGrid API wrapper with custom thread pool size
+   *
+   * @param apiKey is your Twilio SendGrid API Key: https://app.sendgrid.com/settings/api_keys
+   * @param threadPoolSize the pool size to initialize for sending email asynchronously
+   */
+  public SendGrid(final String apiKey, final int threadPoolSize) {
+    initializeSendGrid(apiKey, threadPoolSize);
+  }
+
   /**
    * Construct a new Twilio SendGrid API wrapper.
    *
@@ -25,6 +38,18 @@ public SendGrid(final String apiKey, final Boolean test) {
     initializeSendGrid(apiKey);
   }
 
+  /**
+   * Construct a new Twilio SendGrid API wrapper with custom thread pool size
+   *
+   * @param apiKey is your Twilio SendGrid API Key: https://app.sendgrid.com/settings/api_keys
+   * @param test   is true if you are unit testing
+   * @param threadPoolSize the pool size to initialize for sending email asynchronously
+   */
+  public SendGrid(final String apiKey, final Boolean test, final int threadPoolSize) {
+    super(test);
+    initializeSendGrid(apiKey, threadPoolSize);
+  }
+
   /**
    * Construct a new Twilio SendGrid API wrapper.
    *
@@ -37,11 +62,33 @@ public SendGrid(final String apiKey, final Client client) {
   }
 
   /**
-   * Initialize the client.
+   * Construct a new Twilio SendGrid API wrapper with custom thread pool size
+   *
+   * @param apiKey is your Twilio SendGrid API Key: https://app.sendgrid.com/settings/api_keys
+   * @param client the Client to use (allows to customize its configuration)
+   * @param threadPoolSize the pool size to initialize for sending email asynchronously
+   */
+  public SendGrid(final String apiKey, final Client client, final int threadPoolSize) {
+    super(client);
+    initializeSendGrid(apiKey, threadPoolSize);
+  }
+
+  /**
+   * Initialize the client
    *
    * @param apiKey the user's API key
    */
   public void initializeSendGrid(final String apiKey) {
-    this.initialize("Bearer " + apiKey, "api.sendgrid.com");
+    this.initialize(BEARER + apiKey, SENDGRID_HOST_NAME);
+  }
+
+  /**
+   * Initialize the client with custom thread pool size with custom thread pool size
+   *
+   * @param apiKey the user's API key
+   * @param threadPoolSize the pool size to initialize for sending email asynchronously
+   */
+  public void initializeSendGrid(final String apiKey, final int threadPoolSize) {
+    this.initialize(BEARER + apiKey, SENDGRID_HOST_NAME, threadPoolSize);
   }
 }
diff --git a/src/main/java/com/sendgrid/SendGridAPI.java b/src/main/java/com/sendgrid/SendGridAPI.java
index 71b2c3cc..5ce6d89c 100644
--- a/src/main/java/com/sendgrid/SendGridAPI.java
+++ b/src/main/java/com/sendgrid/SendGridAPI.java
@@ -6,13 +6,22 @@
 public interface SendGridAPI {
 
   /**
-   * Initialize the client.
+   * Initialize the client with default thread pool size
    *
    * @param auth authorization header value
    * @param host the base URL for the API
    */
   void initialize(final String auth, final String host);
 
+  /**
+   * Initialize the client with custom thread pool size
+   *
+   * @param auth authorization header value
+   * @param host the base URL for the API
+   * @param threadPoolSize the pool size to initialize for sending email asynchronously
+   */
+  void initialize(final String auth, final String host, int threadPoolSize);
+
   /**
    * Get the current library version.
    *
diff --git a/src/test/java/com/sendgrid/SendGridTest.java b/src/test/java/com/sendgrid/SendGridTest.java
index 2ac11fdb..d8b490bf 100644
--- a/src/test/java/com/sendgrid/SendGridTest.java
+++ b/src/test/java/com/sendgrid/SendGridTest.java
@@ -31,6 +31,15 @@ public void testInitialization() {
     Assert.assertEquals(sg.getRequestHeaders(), requestHeaders);
   }
 
+  @Test
+  public void testInitializationWithCustomThreadPoolSize() {
+    SendGrid sg = new SendGrid(SENDGRID_API_KEY, 4);
+    Assert.assertEquals(sg.getHost(), "api.sendgrid.com");
+    Assert.assertEquals(sg.getVersion(), "v3");
+    Map<String,String> requestHeaders = buildDefaultHeaders();
+    Assert.assertEquals(sg.getRequestHeaders(), requestHeaders);
+  }
+
   @Test
   public void testConstructWithClient() throws IOException {
     Client client = mock(Client.class);