diff --git a/src/special.js b/src/special.js
new file mode 100644
index 0000000..39f337a
--- /dev/null
+++ b/src/special.js
@@ -0,0 +1,8 @@
+"use strict";
+// $Special: Builder of singleton "atoms".
+
+function $Special(name) {
+  this.name = name;
+}
+
+module.exports = $Special;
diff --git a/src/struct.js b/src/struct.js
new file mode 100644
index 0000000..6717711
--- /dev/null
+++ b/src/struct.js
@@ -0,0 +1,119 @@
+"use strict";
+// "Structures": Simple named-tuple-like records.
+
+var Immutable = require("immutable");
+var $Special = require('./special.js');
+
+/* Defined here rather than elsewhere because we need it in makeConstructor. */
+var __ = new $Special("wildcard"); /* wildcard marker */
+
+function StructureType(label, arity) {
+  this.label = label;
+  this.arity = arity;
+  this.pattern = this.instantiate(Immutable.Repeat(__, arity).toArray());
+
+  var self = this;
+  this.ctor = function () {
+    return self.instantiate(Array.prototype.slice.call(arguments));
+  };
+  this.ctor.meta = this;
+  this.ctor.pattern = this.pattern;
+  this.ctor.isClassOf = function (v) { return self.isClassOf(v); };
+}
+
+function makeConstructor(label, fieldNames) {
+  return new StructureType(label, fieldNames.length).ctor;
+}
+
+StructureType.prototype.equals = function (other) {
+  if (!(other instanceof StructureType)) return false;
+  return this.arity === other.arity && this.label === other.label;
+};
+
+StructureType.prototype.instantiate = function (fields) {
+  return new Structure(this, fields);
+};
+
+StructureType.prototype.isClassOf = function (v) {
+  return v && (v instanceof Structure) && (v.meta.equals(this));
+};
+
+function Structure(meta, fields) {
+  if (!isStructureType(meta)) {
+    throw new Error("Structure: requires structure type");
+  }
+  if (fields.length !== meta.arity) {
+    throw new Error("Structure: cannot instantiate meta "+JSON.stringify(meta.label)+
+                    " expecting "+meta.arity+" fields with "+fields.length+" fields");
+  }
+  this.meta = meta;
+  this.length = meta.arity;
+  this.fields = fields.slice(0);
+  for (var i = 0; i < fields.length; i++) {
+    this[i] = fields[i];
+  }
+}
+
+Structure.prototype.clone = function () {
+  return new Structure(this.meta, this.fields);
+};
+
+Structure.prototype.get = function (index) {
+  return this[index];
+};
+
+Structure.prototype.set = function (index, value) {
+  var s = this.clone();
+  s[index] = s.fields[index] = value;
+};
+
+function reviveStructs(j) {
+  if (Array.isArray(j)) {
+    return j.map(reviveStructs);
+  }
+
+  if ((j !== null) && typeof j === 'object') {
+    if ((typeof j['@type'] === 'string') && Array.isArray(j['fields'])) {
+      return (new StructureType(j['@type'], j['fields'].length)).instantiate(j['fields']);
+    } else {
+      for (var k in j) {
+        if (Object.prototype.hasOwnProperty.call(j, k)) {
+          j[k] = reviveStructs(j[k]);
+        }
+      }
+      return j;
+    }
+  }
+
+  return j;
+}
+
+function reviver(k, v) {
+  if (k === '') {
+    return reviveStructs(v);
+  }
+  return v;
+};
+
+Structure.prototype.toJSON = function () {
+  return { '@type': this.meta.label, 'fields': this.fields };
+};
+
+function isStructureType(v) {
+  return v && (v instanceof StructureType);
+}
+
+function isStructure(v) {
+  return v && (v instanceof Structure);
+}
+
+///////////////////////////////////////////////////////////////////////////
+
+module.exports.__ = __;
+module.exports.StructureType = StructureType;
+module.exports.makeConstructor = makeConstructor;
+module.exports.Structure = Structure;
+module.exports.reviveStructs = reviveStructs;
+module.exports.reviver = reviver;
+module.exports.isStructureType = isStructureType;
+module.exports.isStructure = isStructure;