diff --git a/api.go b/api.go
index 64d2008..8b74f59 100644
--- a/api.go
+++ b/api.go
@@ -9,18 +9,20 @@ import (
 )
 
 type APIClient struct {
-	Key    string
-	URL    string
-	Client *http.Client
+	Key       string
+	URL       string
+	UserAgent string
+	Client    *http.Client
 }
 
 // NewAPIClient prepares a client for use with the Customer.io API, see: https://customer.io/docs/api/#apicoreintroduction
 // using an App API Key from https://fly.customer.io/settings/api_credentials?keyType=app
 func NewAPIClient(key string, opts ...option) *APIClient {
 	client := &APIClient{
-		Key:    key,
-		Client: http.DefaultClient,
-		URL:    "https://api.customer.io",
+		Key:       key,
+		Client:    http.DefaultClient,
+		URL:       "https://api.customer.io",
+		UserAgent: DefaultUserAgent,
 	}
 
 	for _, opt := range opts {
@@ -44,6 +46,7 @@ func (c *APIClient) doRequest(ctx context.Context, verb, requestPath string, bod
 
 	req.Header.Set("Authorization", "Bearer "+c.Key)
 	req.Header.Set("Content-Type", "application/json")
+	req.Header.Add("User-Agent", c.UserAgent)
 
 	resp, err := c.Client.Do(req)
 	if err != nil {
diff --git a/customerio.go b/customerio.go
index 276ca4c..db542ad 100644
--- a/customerio.go
+++ b/customerio.go
@@ -13,12 +13,15 @@ import (
 	"strings"
 )
 
+const DefaultUserAgent = "Customer.io Go Client/" + Version
+
 // CustomerIO wraps the customer.io track API, see: https://customer.io/docs/api/#apitrackintroduction
 type CustomerIO struct {
-	siteID string
-	apiKey string
-	URL    string
-	Client *http.Client
+	siteID    string
+	apiKey    string
+	URL       string
+	UserAgent string
+	Client    *http.Client
 }
 
 // CustomerIOError is returned by any method that fails at the API level
@@ -48,10 +51,11 @@ func NewTrackClient(siteID, apiKey string, opts ...option) *CustomerIO {
 		},
 	}
 	c := &CustomerIO{
-		siteID: siteID,
-		apiKey: apiKey,
-		URL:    "https://track.customer.io",
-		Client: client,
+		siteID:    siteID,
+		apiKey:    apiKey,
+		URL:       "https://track.customer.io",
+		UserAgent: DefaultUserAgent,
+		Client:    client,
 	}
 
 	for _, opt := range opts {
@@ -176,6 +180,7 @@ func (c *CustomerIO) request(method, url string, body interface{}) error {
 			return err
 		}
 
+		req.Header.Add("User-Agent", c.UserAgent)
 		req.Header.Add("Content-Type", "application/json")
 		req.Header.Add("Content-Length", strconv.Itoa(len(j)))
 	} else {
diff --git a/options.go b/options.go
index ffe9c55..9b15896 100644
--- a/options.go
+++ b/options.go
@@ -44,3 +44,14 @@ func WithHTTPClient(client *http.Client) option {
 		},
 	}
 }
+
+func WithUserAgent(ua string) option {
+	return option{
+		api: func(a *APIClient) {
+			a.UserAgent = ua
+		},
+		track: func(c *CustomerIO) {
+			c.UserAgent = ua
+		},
+	}
+}
diff --git a/options_test.go b/options_test.go
index 58bf9b8..f1e1163 100644
--- a/options_test.go
+++ b/options_test.go
@@ -25,6 +25,12 @@ func TestAPIOptions(t *testing.T) {
 	if !reflect.DeepEqual(client.Client, hc) {
 		t.Errorf("wrong http client. got: %#v, want: %#v", client.Client, hc)
 	}
+
+	customUserAgent := "Customer.io"
+	client = customerio.NewAPIClient("mykey", customerio.WithUserAgent(customUserAgent))
+	if client.UserAgent != customUserAgent {
+		t.Errorf("wrong user-agent. got: %s, want: %s", client.UserAgent, customUserAgent)
+	}
 }
 
 func TestTrackOptions(t *testing.T) {
@@ -44,4 +50,10 @@ func TestTrackOptions(t *testing.T) {
 	if !reflect.DeepEqual(client.Client, hc) {
 		t.Errorf("wrong http client. got: %#v, want: %#v", client.Client, hc)
 	}
+
+	customUserAgent := "Customer.io"
+	client = customerio.NewTrackClient("site_id", "api_key", customerio.WithUserAgent(customUserAgent))
+	if client.UserAgent != customUserAgent {
+		t.Errorf("wrong user-agent. got: %s, want: %s", client.UserAgent, customUserAgent)
+	}
 }
diff --git a/version.go b/version.go
new file mode 100644
index 0000000..e122cd4
--- /dev/null
+++ b/version.go
@@ -0,0 +1,3 @@
+package customerio
+
+const Version = "3.2.0"