diff --git a/doc/langdef.md b/doc/langdef.md
index 8f618e9e..0ab6481a 100644
--- a/doc/langdef.md
+++ b/doc/langdef.md
@@ -1835,7 +1835,7 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
     </td>
   </tr>
   <tr>
-    <th rowspan="1">
+    <th rowspan="2">
       bool
     </th>
     <td>
@@ -1846,7 +1846,15 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
     </td>
   </tr>
   <tr>
-    <th rowspan="2">
+    <td>
+      (bool) -> bool
+    </td>
+    <td>
+      identity
+    </td>
+  </tr>
+  <tr>
+    <th rowspan="3">
       bytes
     </th>
     <td>
@@ -1856,6 +1864,14 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
       type denotation
     </td>
   </tr>
+  <tr>
+    <td>
+      (bytes) -> bytes
+    </td>
+    <td>
+      identity
+    </td>
+  </tr>
   <tr>
     <td>
       (string) -> bytes
@@ -1877,7 +1893,7 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
     </td>
   </tr>
   <tr>
-    <th rowspan="4">
+    <th rowspan="5">
       double
     </th>
     <td>
@@ -1887,6 +1903,14 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
       type denotation
     </td>
   </tr>
+  <tr>
+    <td>
+      (double) -> double
+    </td>
+    <td>
+      identity
+    </td>
+  </tr>
   <tr>
     <td>
       (int) -> double
@@ -1912,9 +1936,17 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
     </td>
   </tr>
   <tr>
-    <th rowspan="1">
+    <th rowspan="2">
       duration
     </th>
+    <td>
+      (google.protobuf.Duration) -> google.protobuf.Duration
+    </td>
+    <td>
+      identity
+    </td>
+  </tr>
+  <tr>
     <td>
       (string) -> google.protobuf.Duration
     </td>
@@ -2180,7 +2212,7 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
     </td>
   </tr>
   <tr>
-    <th rowspan="6">
+    <th rowspan="7">
       int
     </th>
     <td>
@@ -2190,6 +2222,14 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
       type denotation
     </td>
   </tr>
+  <tr>
+    <td>
+      (int) -> int
+    </td>
+    <td>
+      identity
+    </td>
+  </tr>
   <tr>
     <td>
       (uint) -> int
@@ -2333,7 +2373,7 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
     </td>
   </tr>
   <tr>
-    <th rowspan="7">
+    <th rowspan="8">
       string
     </th>
     <td>
@@ -2343,6 +2383,14 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
       type denotation
     </td>
   </tr>
+  <tr>
+    <td>
+      (string) -> string
+    </td>
+    <td>
+      identity
+    </td>
+  </tr>
   <tr>
     <td>
       (int) -> string
@@ -2392,9 +2440,17 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
     </td>
   </tr>
   <tr>
-    <th rowspan="1">
+    <th rowspan="2">
       timestamp
     </th>
+    <td>
+      (google.protobuf.Timestamp) -> google.protobuf.Timestamp
+    </td>
+    <td>
+      identity
+    </td>
+  </tr>
+  <tr>
     <td>
       (string) -> google.protobuf.Timestamp
     </td>
@@ -2433,6 +2489,14 @@ See [cel-go/issues/9](https://github.com/google/cel-go/issues/9).
       type denotation
     </td>
   </tr>
+  <tr>
+    <td>
+      (uint) -> uint
+    </td>
+    <td>
+      identity
+    </td>
+  </tr>
   <tr>
     <td>
       (int) -> uint
diff --git a/tests/simple/testdata/conversions.textproto b/tests/simple/testdata/conversions.textproto
index 87820564..75ffdddd 100644
--- a/tests/simple/testdata/conversions.textproto
+++ b/tests/simple/testdata/conversions.textproto
@@ -505,3 +505,47 @@ section {
     value: { uint64_value: 300 }
   }
 }
+section {
+  name: "identity"
+  description: "Identity functions"
+  test {
+    name: "bool"
+    expr: "bool(true)"
+    value: { bool_value: true }
+  }
+  test {
+    name: "int"
+    expr: "int(1)"
+    value: { int64_value: 1 }
+  }
+  test {
+    name: "uint"
+    expr: "uint(1u)"
+    value: { uint64_value: 1 }
+  }
+  test {
+    name: "double"
+    expr: "double(5.5)"
+    value: { double_value: 5.5 }
+  }
+  test {
+    name: "string"
+    expr: "string('hello')"
+    value: { string_value: "hello" }
+  }
+  test {
+    name: "bytes"
+    expr: "bytes(bytes('abc'))"
+    value: { bytes_value: "abc" }
+  }
+  test {
+    name: "duration"
+    expr: "duration(duration('100s')) == duration('100s')"
+    value: { bool_value: true }
+  }
+  test {
+    name: "timestamp"
+    expr: "timestamp(timestamp(1000000000)) == timestamp(1000000000)"
+    value: { bool_value: true }
+  }
+}