diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5335206..ccae9df 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,8 +9,12 @@ Versioning].
 
 ## [Unreleased] <!-- #release:date -->
 
+* Add support for Plan metadata.
+
 ## [0.6.0] - 2023-05-12
 
+* Modified the `InvoiceSubscription` field to be optional.
+
 ## [0.5.0] - 2023-05-11
 
 * Add `amount_due` as part of `Invoice`.
diff --git a/src/client/plans.rs b/src/client/plans.rs
index bec5f3e..2b0adaa 100644
--- a/src/client/plans.rs
+++ b/src/client/plans.rs
@@ -13,6 +13,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::collections::BTreeMap;
+
 use futures_core::Stream;
 use reqwest::Method;
 use serde::{Deserialize, Serialize};
@@ -58,6 +60,9 @@ pub struct Plan {
     /// The time at which the plan was created.
     #[serde(with = "time::serde::rfc3339")]
     pub created_at: OffsetDateTime,
+    /// Arbitrary metadata that is attached to the plan. Cannot be nested, must have string values.
+    #[serde(default)]
+    pub metadata: BTreeMap<String, String>,
     // TODO: many missing fields.
 }
 
diff --git a/tests/api.rs b/tests/api.rs
index 187e6a2..93f6d6c 100644
--- a/tests/api.rs
+++ b/tests/api.rs
@@ -503,6 +503,10 @@ async fn test_subscriptions() {
 
         assert_eq!(subscription.customer.id, customer.id);
         assert_eq!(subscription.plan.external_id.as_deref(), Some("test"));
+        assert_eq!(
+            subscription.plan.metadata.get("purpose"),
+            Some(&"test".to_string())
+        );
         assert_eq!(subscription.net_terms, 3);
         assert!(subscription.auto_collection);