diff --git a/hugr-cli/src/extensions.rs b/hugr-cli/src/extensions.rs
index 757dba21f..8370e5648 100644
--- a/hugr-cli/src/extensions.rs
+++ b/hugr-cli/src/extensions.rs
@@ -27,7 +27,7 @@ impl ExtArgs {
     pub fn run_dump(&self) {
         let base_dir = &self.outdir;
 
-        for (name, ext) in hugr_core::std_extensions::std_reg().into_iter() {
+        for (name, ext) in hugr_core::std_extensions::STD_REG.iter() {
             let mut path = base_dir.clone();
             for part in name.split('.') {
                 path.push(part);
diff --git a/hugr-cli/src/validate.rs b/hugr-cli/src/validate.rs
index b603365fe..2e226fb08 100644
--- a/hugr-cli/src/validate.rs
+++ b/hugr-cli/src/validate.rs
@@ -57,7 +57,7 @@ impl HugrArgs {
         let mut reg: ExtensionRegistry = if self.no_std {
             hugr_core::extension::PRELUDE_REGISTRY.to_owned()
         } else {
-            hugr_core::std_extensions::std_reg()
+            hugr_core::std_extensions::STD_REG.to_owned()
         };
 
         // register packed extensions
diff --git a/hugr-core/src/std_extensions.rs b/hugr-core/src/std_extensions.rs
index 8ce690674..a6738ddff 100644
--- a/hugr-core/src/std_extensions.rs
+++ b/hugr-core/src/std_extensions.rs
@@ -18,8 +18,14 @@ pub fn std_reg() -> ExtensionRegistry {
         arithmetic::conversions::EXTENSION.to_owned(),
         arithmetic::float_ops::EXTENSION.to_owned(),
         arithmetic::float_types::EXTENSION.to_owned(),
+        collections::EXTENSION.to_owned(),
         logic::EXTENSION.to_owned(),
         ptr::EXTENSION.to_owned(),
     ])
     .unwrap()
 }
+
+lazy_static::lazy_static! {
+    /// Standard extension registry.
+    pub static ref STD_REG: ExtensionRegistry = std_reg();
+}
diff --git a/hugr-core/src/std_extensions/collections.rs b/hugr-core/src/std_extensions/collections.rs
index 3c4677f5c..480780496 100644
--- a/hugr-core/src/std_extensions/collections.rs
+++ b/hugr-core/src/std_extensions/collections.rs
@@ -30,7 +30,7 @@ pub const POP_NAME: OpName = OpName::new_inline("pop");
 /// Push operation name.
 pub const PUSH_NAME: OpName = OpName::new_inline("push");
 /// Reported unique name of the extension
-pub const EXTENSION_NAME: ExtensionId = ExtensionId::new_unchecked("Collections");
+pub const EXTENSION_NAME: ExtensionId = ExtensionId::new_unchecked("collections");
 /// Extension version.
 pub const VERSION: semver::Version = semver::Version::new(0, 1, 0);
 
diff --git a/specification/std_extensions/collections.json b/specification/std_extensions/collections.json
new file mode 100644
index 000000000..6263c2074
--- /dev/null
+++ b/specification/std_extensions/collections.json
@@ -0,0 +1,143 @@
+{
+  "version": "0.1.0",
+  "name": "collections",
+  "extension_reqs": [],
+  "types": {
+    "List": {
+      "extension": "collections",
+      "name": "List",
+      "params": [
+        {
+          "tp": "Type",
+          "b": "A"
+        }
+      ],
+      "description": "Generic dynamically sized list of type T.",
+      "bound": {
+        "b": "FromParams",
+        "indices": [
+          0
+        ]
+      }
+    }
+  },
+  "values": {},
+  "operations": {
+    "pop": {
+      "extension": "collections",
+      "name": "pop",
+      "description": "Pop from back of list",
+      "signature": {
+        "params": [
+          {
+            "tp": "Type",
+            "b": "A"
+          }
+        ],
+        "body": {
+          "input": [
+            {
+              "t": "Opaque",
+              "extension": "collections",
+              "id": "List",
+              "args": [
+                {
+                  "tya": "Type",
+                  "ty": {
+                    "t": "V",
+                    "i": 0,
+                    "b": "A"
+                  }
+                }
+              ],
+              "bound": "A"
+            }
+          ],
+          "output": [
+            {
+              "t": "Opaque",
+              "extension": "collections",
+              "id": "List",
+              "args": [
+                {
+                  "tya": "Type",
+                  "ty": {
+                    "t": "V",
+                    "i": 0,
+                    "b": "A"
+                  }
+                }
+              ],
+              "bound": "A"
+            },
+            {
+              "t": "V",
+              "i": 0,
+              "b": "A"
+            }
+          ],
+          "extension_reqs": []
+        }
+      },
+      "binary": false
+    },
+    "push": {
+      "extension": "collections",
+      "name": "push",
+      "description": "Push to back of list",
+      "signature": {
+        "params": [
+          {
+            "tp": "Type",
+            "b": "A"
+          }
+        ],
+        "body": {
+          "input": [
+            {
+              "t": "Opaque",
+              "extension": "collections",
+              "id": "List",
+              "args": [
+                {
+                  "tya": "Type",
+                  "ty": {
+                    "t": "V",
+                    "i": 0,
+                    "b": "A"
+                  }
+                }
+              ],
+              "bound": "A"
+            },
+            {
+              "t": "V",
+              "i": 0,
+              "b": "A"
+            }
+          ],
+          "output": [
+            {
+              "t": "Opaque",
+              "extension": "collections",
+              "id": "List",
+              "args": [
+                {
+                  "tya": "Type",
+                  "ty": {
+                    "t": "V",
+                    "i": 0,
+                    "b": "A"
+                  }
+                }
+              ],
+              "bound": "A"
+            }
+          ],
+          "extension_reqs": []
+        }
+      },
+      "binary": false
+    }
+  }
+}