diff --git a/crates/rmcp/src/model.rs b/crates/rmcp/src/model.rs
index fa47ea788..0b7c314b1 100644
--- a/crates/rmcp/src/model.rs
+++ b/crates/rmcp/src/model.rs
@@ -889,6 +889,15 @@ impl Default for ClientInfo {
     }
 }
 
+/// Icon themes supported by the MCP specification
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Copy)]
+#[serde(rename_all = "lowercase")] //match spec
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub enum IconTheme {
+    Light,
+    Dark,
+}
+
 /// A URL pointing to an icon resource or a base64-encoded data URI.
 ///
 /// Clients that support rendering icons MUST support at least the following MIME types:
@@ -911,6 +920,9 @@ pub struct Icon {
     /// Size specification, each string should be in WxH format (e.g., `\"48x48\"`, `\"96x96\"`) or `\"any\"` for scalable formats like SVG
     #[serde(skip_serializing_if = "Option::is_none")]
     pub sizes: Option<Vec<String>>,
+    /// Optional specifier for the theme this icon is designed for
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub theme: Option<IconTheme>,
 }
 
 impl Icon {
@@ -920,6 +932,7 @@ impl Icon {
             src: src.into(),
             mime_type: None,
             sizes: None,
+            theme: None,
         }
     }
 
@@ -934,6 +947,12 @@ impl Icon {
         self.sizes = Some(sizes);
         self
     }
+
+    /// Set the theme.
+    pub fn with_theme(mut self, theme: IconTheme) -> Self {
+        self.theme = Some(theme);
+        self
+    }
 }
 
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
@@ -3642,12 +3661,14 @@ mod tests {
             src: "https://example.com/icon.png".to_string(),
             mime_type: Some("image/png".to_string()),
             sizes: Some(vec!["48x48".to_string()]),
+            theme: Some(IconTheme::Light),
         };
 
         let json = serde_json::to_value(&icon).unwrap();
         assert_eq!(json["src"], "https://example.com/icon.png");
         assert_eq!(json["mimeType"], "image/png");
         assert_eq!(json["sizes"][0], "48x48");
+        assert_eq!(json["theme"], "light");
 
         // Test deserialization
         let deserialized: Icon = serde_json::from_value(json).unwrap();
@@ -3660,12 +3681,14 @@ mod tests {
             src: "data:image/svg+xml;base64,PHN2Zy8+".to_string(),
             mime_type: None,
             sizes: None,
+            theme: None,
         };
 
         let json = serde_json::to_value(&icon).unwrap();
         assert_eq!(json["src"], "data:image/svg+xml;base64,PHN2Zy8+");
         assert!(json.get("mimeType").is_none());
         assert!(json.get("sizes").is_none());
+        assert!(json.get("theme").is_none());
     }
 
     #[test]
@@ -3680,11 +3703,13 @@ mod tests {
                     src: "https://example.com/icon.png".to_string(),
                     mime_type: Some("image/png".to_string()),
                     sizes: Some(vec!["48x48".to_string()]),
+                    theme: Some(IconTheme::Dark),
                 },
                 Icon {
                     src: "https://example.com/icon.svg".to_string(),
                     mime_type: Some("image/svg+xml".to_string()),
                     sizes: Some(vec!["any".to_string()]),
+                    theme: Some(IconTheme::Light),
                 },
             ]),
             website_url: Some("https://example.com".to_string()),
@@ -3699,6 +3724,8 @@ mod tests {
         assert_eq!(json["icons"][0]["sizes"][0], "48x48");
         assert_eq!(json["icons"][1]["mimeType"], "image/svg+xml");
         assert_eq!(json["icons"][1]["sizes"][0], "any");
+        assert_eq!(json["icons"][0]["theme"], "dark");
+        assert_eq!(json["icons"][1]["theme"], "light");
     }
 
     #[test]
@@ -3731,6 +3758,7 @@ mod tests {
                     src: "https://example.com/server.png".to_string(),
                     mime_type: Some("image/png".to_string()),
                     sizes: Some(vec!["48x48".to_string()]),
+                    theme: Some(IconTheme::Light),
                 }]),
                 website_url: Some("https://docs.example.com".to_string()),
             },
@@ -3744,6 +3772,7 @@ mod tests {
             "https://example.com/server.png"
         );
         assert_eq!(json["serverInfo"]["icons"][0]["sizes"][0], "48x48");
+        assert_eq!(json["serverInfo"]["icons"][0]["theme"], "light");
         assert_eq!(json["serverInfo"]["websiteUrl"], "https://docs.example.com");
     }
 
diff --git a/crates/rmcp/src/model/resource.rs b/crates/rmcp/src/model/resource.rs
index 8a25e25ba..2e004d679 100644
--- a/crates/rmcp/src/model/resource.rs
+++ b/crates/rmcp/src/model/resource.rs
@@ -214,6 +214,7 @@ mod tests {
     use serde_json;
 
     use super::*;
+    use crate::model::IconTheme;
 
     #[test]
     fn test_resource_serialization() {
@@ -265,6 +266,7 @@ mod tests {
                 src: "https://example.com/icon.png".to_string(),
                 mime_type: Some("image/png".to_string()),
                 sizes: Some(vec!["48x48".to_string()]),
+                theme: Some(IconTheme::Light),
             }]),
         };
 
@@ -272,6 +274,7 @@ mod tests {
         assert!(json["icons"].is_array());
         assert_eq!(json["icons"][0]["src"], "https://example.com/icon.png");
         assert_eq!(json["icons"][0]["sizes"][0], "48x48");
+        assert_eq!(json["icons"][0]["theme"], "light");
     }
 
     #[test]
diff --git a/crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema.json b/crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema.json
index 940f03f1b..f8cac1fcd 100644
--- a/crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema.json
+++ b/crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema.json
@@ -720,12 +720,31 @@
         "src": {
           "description": "A standard URI pointing to an icon resource",
           "type": "string"
+        },
+        "theme": {
+          "description": "Optional specifier for the theme this icon is designed for",
+          "anyOf": [
+            {
+              "$ref": "#/definitions/IconTheme"
+            },
+            {
+              "type": "null"
+            }
+          ]
         }
       },
       "required": [
         "src"
       ]
     },
+    "IconTheme": {
+      "description": "Icon themes supported by the MCP specification",
+      "type": "string",
+      "enum": [
+        "light",
+        "dark"
+      ]
+    },
     "Implementation": {
       "type": "object",
       "properties": {
diff --git a/crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema_current.json b/crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema_current.json
index 940f03f1b..f8cac1fcd 100644
--- a/crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema_current.json
+++ b/crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema_current.json
@@ -720,12 +720,31 @@
         "src": {
           "description": "A standard URI pointing to an icon resource",
           "type": "string"
+        },
+        "theme": {
+          "description": "Optional specifier for the theme this icon is designed for",
+          "anyOf": [
+            {
+              "$ref": "#/definitions/IconTheme"
+            },
+            {
+              "type": "null"
+            }
+          ]
         }
       },
       "required": [
         "src"
       ]
     },
+    "IconTheme": {
+      "description": "Icon themes supported by the MCP specification",
+      "type": "string",
+      "enum": [
+        "light",
+        "dark"
+      ]
+    },
     "Implementation": {
       "type": "object",
       "properties": {
diff --git a/crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema.json b/crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema.json
index bd8f744b0..b5a134c32 100644
--- a/crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema.json
+++ b/crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema.json
@@ -1090,12 +1090,31 @@
         "src": {
           "description": "A standard URI pointing to an icon resource",
           "type": "string"
+        },
+        "theme": {
+          "description": "Optional specifier for the theme this icon is designed for",
+          "anyOf": [
+            {
+              "$ref": "#/definitions/IconTheme"
+            },
+            {
+              "type": "null"
+            }
+          ]
         }
       },
       "required": [
         "src"
       ]
     },
+    "IconTheme": {
+      "description": "Icon themes supported by the MCP specification",
+      "type": "string",
+      "enum": [
+        "light",
+        "dark"
+      ]
+    },
     "Implementation": {
       "type": "object",
       "properties": {
diff --git a/crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema_current.json b/crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema_current.json
index bd8f744b0..b5a134c32 100644
--- a/crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema_current.json
+++ b/crates/rmcp/tests/test_message_schema/server_json_rpc_message_schema_current.json
@@ -1090,12 +1090,31 @@
         "src": {
           "description": "A standard URI pointing to an icon resource",
           "type": "string"
+        },
+        "theme": {
+          "description": "Optional specifier for the theme this icon is designed for",
+          "anyOf": [
+            {
+              "$ref": "#/definitions/IconTheme"
+            },
+            {
+              "type": "null"
+            }
+          ]
         }
       },
       "required": [
         "src"
       ]
     },
+    "IconTheme": {
+      "description": "Icon themes supported by the MCP specification",
+      "type": "string",
+      "enum": [
+        "light",
+        "dark"
+      ]
+    },
     "Implementation": {
       "type": "object",
       "properties": {