diff --git a/README.md b/README.md
index fb72d53..3f43173 100644
--- a/README.md
+++ b/README.md
@@ -439,6 +439,42 @@ rescue Customerio::InvalidResponse => e
 end
 ```
 
+#### WhatsApp
+
+Create a new `SendWhatsAppRequest` object containing:
+
+* `transactional_message_id`: the ID or trigger name of the transactional message you want to send.
+* an `identifiers` object containing the `id` or `email` of your recipient. If the profile does not exist, Customer.io creates it.
+
+`to` is the WhatsApp number in E.164 format.
+
+Use `send_whatsapp` referencing your request to send a transactional message. [Learn more about transactional messages and `SendWhatsAppRequest` properties](https://customer.io/docs/transactional-api).
+
+
+```ruby
+require "customerio"
+
+client = Customerio::APIClient.new("your API key", region: Customerio::Regions::US)
+
+request = Customerio::SendWhatsAppRequest.new(
+  transactional_message_id: "3",
+  to: "+15551234567",
+  message_data: {
+    name: "Person",
+  },
+  identifiers: {
+    id: "2",
+  },
+)
+
+begin
+  response = client.send_whatsapp(request)
+  puts response
+rescue Customerio::InvalidResponse => e
+  puts e.code, e.message
+end
+```
+
 ### Trigger Broadcasts
 
 You can trigger [API-triggered broadcasts](https://customer.io/docs/api-triggered-broadcasts/) using the `APIClient`. Create a `TriggerBroadcastRequest` with the broadcast's numeric ID and optional audience/data parameters.
diff --git a/lib/customerio.rb b/lib/customerio.rb
index 641113b..98bed86 100644
--- a/lib/customerio.rb
+++ b/lib/customerio.rb
@@ -9,6 +9,7 @@ module Customerio
   require "customerio/requests/send_email_request"
   require "customerio/requests/send_push_request"
   require "customerio/requests/send_sms_request"
+  require "customerio/requests/send_whatsapp_request"
   require "customerio/requests/send_inbox_message_request"
   require "customerio/requests/send_in_app_request"
   require "customerio/requests/trigger_broadcast_request"
diff --git a/lib/customerio/api.rb b/lib/customerio/api.rb
index 54fa007..7c373b7 100644
--- a/lib/customerio/api.rb
+++ b/lib/customerio/api.rb
@@ -34,6 +34,12 @@ def send_sms(req)
       deliver(send_sms_path, req.message)
     end
 
+    def send_whatsapp(req)
+      validate_request!(req, SendWhatsAppRequest)
+
+      deliver(send_whatsapp_path, req.message)
+    end
+
     def send_inbox_message(req)
       validate_request!(req, SendInboxMessageRequest)
 
@@ -86,6 +92,10 @@ def send_sms_path
       "/v1/send/sms"
     end
 
+    def send_whatsapp_path
+      "/v1/send/whatsapp"
+    end
+
     def send_inbox_message_path
       "/v1/send/inbox_message"
     end
diff --git a/lib/customerio/requests/send_whatsapp_request.rb b/lib/customerio/requests/send_whatsapp_request.rb
new file mode 100644
index 0000000..ede2afd
--- /dev/null
+++ b/lib/customerio/requests/send_whatsapp_request.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+require "base64"
+
+module Customerio
+  class SendWhatsAppRequest
+    REQUIRED_FIELDS = %i[identifiers transactional_message_id].freeze
+
+    OPTIONAL_FIELDS = %i[
+      message_data
+      to
+      disable_message_retention
+      send_to_unsubscribed
+      tracked
+      queue_draft
+      send_at
+      language
+    ].freeze
+
+    attr_reader :message
+
+    def initialize(opts)
+      @message = opts.select { |field, _value| valid_field?(field) }
+      @message[:attachments] ||= {}
+    end
+
+    def attach(name, data, encode: true)
+      raise ArgumentError, "attachment #{name} already exists" if @message[:attachments].key?(name)
+
+      @message[:attachments][name] = encode ? Base64.strict_encode64(data) : data
+    end
+
+    private
+
+    def valid_field?(field)
+      REQUIRED_FIELDS.include?(field) || OPTIONAL_FIELDS.include?(field)
+    end
+  end
+end
diff --git a/spec/api_client_spec.rb b/spec/api_client_spec.rb
index fb098b0..a961666 100644
--- a/spec/api_client_spec.rb
+++ b/spec/api_client_spec.rb
@@ -312,6 +312,68 @@ def json(data)
     end
   end
 
+  describe "#send_whatsapp" do
+    it "sends a POST request to the /api/send/whatsapp path" do
+      req = Customerio::SendWhatsAppRequest.new(
+        identifiers: {
+          id: 'c1',
+        },
+        transactional_message_id: 1,
+        to: '+15551234567',
+        from: '+15559876543',
+        tracked: true,
+      )
+
+      stub_request(:post, api_uri('/v1/send/whatsapp'))
+        .with(headers: request_headers, body: req.message)
+        .to_return(status: 200, body: { delivery_id: 1 }.to_json, headers: {})
+
+      expect(client.send_whatsapp(req)).to eq({ "delivery_id" => 1 })
+    end
+
+    it "handles validation failures (400)" do
+      req = Customerio::SendWhatsAppRequest.new(
+        identifiers: {
+          id: 'c1',
+        },
+        transactional_message_id: 1,
+      )
+
+      err_json = { meta: { error: "example error" } }.to_json
+
+      stub_request(:post, api_uri('/v1/send/whatsapp'))
+        .with(headers: request_headers, body: req.message)
+        .to_return(status: 400, body: err_json, headers: {})
+
+      expect { client.send_whatsapp(req) }.to(
+        raise_error(Customerio::InvalidResponse) { |error|
+      expect(error.message).to eq("example error")
+      expect(error.code).to eq("400")
+        }
+      )
+    end
+
+    it "handles other failures (5xx)" do
+      req = Customerio::SendWhatsAppRequest.new(
+        identifiers: {
+          id: 'c1',
+        },
+        transactional_message_id: 1,
+      )
+
+      stub_request(:post, api_uri('/v1/send/whatsapp'))
+        .with(headers: request_headers, body: req.message)
+        .to_return(status: 500, body: "Server unavailable", headers: {})
+
+      expect { client.send_whatsapp(req) }.to(
+        raise_error(Customerio::InvalidResponse) { |error|
+      expect(error.message).to eq("Server unavailable")
+      expect(error.code).to eq("500")
+        }
+      )
+    end
+  end
+
   describe "#send_inbox_message" do
     it "sends a POST request to the /api/send/inbox_message path" do
       req = Customerio::SendInboxMessageRequest.new(