diff --git a/polyfills/Iterator/prototype/chunks/config.toml b/polyfills/Iterator/prototype/chunks/config.toml
new file mode 100644
index 000000000..f2fc233f5
--- /dev/null
+++ b/polyfills/Iterator/prototype/chunks/config.toml
@@ -0,0 +1,33 @@
+aliases = [ "es2027" ]
+dependencies = [
+	"_ESAbstract.CreateIterResultObject",
+	"_ESAbstract.CreateMethodProperty",
+	"_ESAbstract.Get",
+	"_ESAbstract.IsInteger",
+	"_ESAbstract.IteratorClose",
+	"_ESAbstract.IteratorStepValue",
+	"_ESAbstract.NormalCompletion",
+	"_ESAbstract.ThrowCompletion",
+	"_ESAbstract.Type",
+	"Iterator",
+	"Iterator.prototype.take",
+	"Symbol.iterator",
+]
+spec = "https://tc39.es/ecma262/#sec-iterator.prototype.chunks"
+docs = "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator/chunks"
+
+[browsers]
+android = "*"
+bb = "*"
+chrome = "*"
+edge = "*"
+edge_mob = "*"
+firefox = "<154"
+firefox_mob = "<154"
+ie = "*"
+ie_mob = "*"
+opera = "*"
+op_mob = "*"
+safari = "*"
+ios_saf = "*"
+samsung_mob = "*"
diff --git a/polyfills/Iterator/prototype/chunks/detect.js b/polyfills/Iterator/prototype/chunks/detect.js
new file mode 100644
index 000000000..79e2b91e1
--- /dev/null
+++ b/polyfills/Iterator/prototype/chunks/detect.js
@@ -0,0 +1 @@
+"Iterator" in self && "chunks" in self.Iterator.prototype;
diff --git a/polyfills/Iterator/prototype/chunks/polyfill.js b/polyfills/Iterator/prototype/chunks/polyfill.js
new file mode 100644
index 000000000..b63aca329
--- /dev/null
+++ b/polyfills/Iterator/prototype/chunks/polyfill.js
@@ -0,0 +1,115 @@
+/* global CreateIterResultObject, CreateMethodProperty, Get, IsInteger, Iterator, IteratorClose, IteratorStepValue, NormalCompletion, Symbol, ThrowCompletion, Type */
+
+var IteratorHelperPrototype = (function () {
+	var iterator = Object.create(Iterator.prototype);
+	iterator[Symbol.iterator] = function () {
+		return {
+			next: function () {
+				return { value: undefined, done: true };
+			}
+		};
+	};
+	// use `Iterator.prototype.take` as a way to get `IteratorHelperPrototype`
+	var iteratorHelper = iterator.take(0);
+	return Object.getPrototypeOf(iteratorHelper);
+})();
+
+// 27.1.3.3.1 Iterator.prototype.chunks ( chunkSize )
+CreateMethodProperty(Iterator.prototype, "chunks", function chunks(chunkSize) {
+	// 1. Let obj be the this value.
+	var obj = this;
+	// 2. If obj is not an Object, throw a TypeError exception.
+	if (Type(obj) !== "object") {
+		throw new TypeError("`this` is not an object");
+	}
+	// 3. Let iterated be the Iterator Record { [[Iterator]]: obj, [[NextMethod]]: undefined, [[Done]]: false }.
+	var iterated = {
+		"[[Iterator]]": obj,
+		"[[NextMethod]]": undefined,
+		"[[Done]]": false
+	};
+	// 4. If chunkSize is not an integral Number, then
+	if (!IsInteger(chunkSize)) {
+		// a. Let error be ThrowCompletion(a newly created TypeError object).
+		var error = ThrowCompletion(new TypeError("`chunkSize` is not an integer"));
+		// b. Return ? IteratorClose(iterated, error).
+		return IteratorClose(iterated, error);
+	}
+	// 5. If chunkSize is not in the inclusive interval from 1𝔽 to 𝔽(2**32 - 1), then
+	if (chunkSize < 1 || chunkSize > Math.pow(2, 32) - 1) {
+		// a. Let error be ThrowCompletion(a newly created RangeError object).
+		error = ThrowCompletion(new RangeError("`chunkSize` is invalid"));
+		// b. Return ? IteratorClose(iterated, error).
+		return IteratorClose(iterated, error);
+	}
+	// 6. Set iterated to ? GetIteratorDirect(obj).
+	iterated = {
+		"[[Iterator]]": obj,
+		"[[NextMethod]]": Get(obj, "next"),
+		"[[Done]]": false
+	};
+	// 7. Let closure be a new Abstract Closure with no parameters that captures iterated and chunkSize and performs the following steps when called:
+	// 8. Let result be CreateIteratorFromClosure(closure, "Iterator Helper", %IteratorHelperPrototype%, « [[UnderlyingIterators]] »).
+	var result = Object.create(IteratorHelperPrototype);
+	result["[[Done]]"] = false;
+
+	// a. Let buffer be a new empty List.
+	var buffer = [];
+
+	CreateMethodProperty(result, "next", function () {
+		if (this["[[Done]]"] === true) {
+			return CreateIterResultObject(undefined, true);
+		}
+
+		// b. Repeat,
+		while (true) {
+			// i. Let value be ? IteratorStepValue(iterated).
+			try {
+				var value = IteratorStepValue(iterated);
+			} catch (_error) {
+				this["[[Done]]"] = true;
+				throw _error;
+			}
+			// ii. If value is DONE, then
+			if (value === IteratorStepValue.DONE) {
+				this["[[Done]]"] = true;
+				// 1. If buffer is not empty, then
+				if (buffer.length > 0) {
+					// a. Perform Completion(Yield(CreateArrayFromList(buffer))).
+					return CreateIterResultObject(buffer.slice(), true);
+				}
+				// 2. Return ReturnCompletion(undefined).
+				return CreateIterResultObject(undefined, true);
+			}
+			// iii. Append value to buffer.
+			buffer.push(value);
+			// iv. If the number of elements in buffer is ℝ(chunkSize), then
+			if (buffer.length === chunkSize) {
+				// 1. Let completion be Completion(Yield(CreateArrayFromList(buffer))).
+				try {
+					var completion = CreateIterResultObject(buffer.slice(), false);
+				}
+				// 2. IfAbruptCloseIterator(completion, iterated).
+				catch (err) {
+					this["[[Done]]"] = true;
+					return IteratorClose(iterated, ThrowCompletion(err));
+				}
+				// 3. Set buffer to a new empty List.
+				buffer = [];
+				return completion;
+			}
+		}
+	});
+
+	CreateMethodProperty(result, "return", function (value) {
+		if (this["[[Done]]"] !== true) {
+			IteratorClose(iterated, NormalCompletion(value));
+			this["[[Done]]"] = true;
+		}
+		return CreateIterResultObject(undefined, true);
+	});
+
+	// 9. Set result.[[UnderlyingIterators]] to « iterated ».
+	// 10. Return result.
+	return result;
+});
diff --git a/polyfills/Iterator/prototype/chunks/polyfill.test.js b/polyfills/Iterator/prototype/chunks/polyfill.test.js
new file mode 100644
index 000000000..5d7e5158b
--- /dev/null
+++ b/polyfills/Iterator/prototype/chunks/polyfill.test.js
@@ -0,0 +1,75 @@
+/* global Iterator */
+
+it("is a function", function () {
+	proclaim.isFunction(Iterator.prototype.chunks);
+});
+
+it("has correct arity", function () {
+	proclaim.arity(Iterator.prototype.chunks, 1);
+});
+
+it("has correct name", function () {
+	proclaim.hasName(Iterator.prototype.chunks, "chunks");
+});
+
+it("is not enumerable", function () {
+	proclaim.isNotEnumerable(Iterator.prototype, "chunks");
+});
+
+describe("chunks", function () {
+	function TestIterator(arr) {
+		var i = -1;
+		this.next = function () {
+			i++;
+			if (arr[i] === "error") {
+				throw new Error("uh oh");
+			}
+			return { value: arr[i], done: i >= arr.length };
+		};
+	}
+	TestIterator.prototype = Iterator.prototype;
+
+	it("should chunk an iterator", function () {
+		var iter = new TestIterator([1, 2, 3]).chunks(2);
+		proclaim.deepStrictEqual(iter.next().value, [1, 2]);
+		proclaim.deepStrictEqual(iter.next().value, [3]);
+		proclaim.equal(iter.next().value, undefined);
+
+		iter = new TestIterator([1, 2, 3, 4]).chunks(2);
+		proclaim.deepStrictEqual(iter.next().value, [1, 2]);
+		proclaim.deepStrictEqual(iter.next().value, [3, 4]);
+		proclaim.equal(iter.next().value, undefined);
+	});
+
+	it("should throw for invalid `chunkSize`", function () {
+		proclaim.throws(function () {
+			new TestIterator([1, 2, 3]).chunks(NaN);
+		}, TypeError);
+		proclaim.throws(function () {
+			new TestIterator([1, 2, 3]).chunks(1.5);
+		}, TypeError);
+		proclaim.throws(function () {
+			new TestIterator([1, 2, 3]).chunks(0);
+		}, RangeError);
+		proclaim.throws(function () {
+			new TestIterator([1, 2, 3]).chunks(Math.pow(2, 32));
+		}, RangeError);
+	});
+
+	it("should handle errors during iteration", function () {
+		var iter = new TestIterator([1, 2, "error", 4]).chunks(1);
+		proclaim.deepStrictEqual(iter.next().value, [1]);
+		proclaim.deepStrictEqual(iter.next().value, [2]);
+		proclaim.throws(function () {
+			iter.next();
+		}, Error);
+		proclaim.equal(iter.next().value, undefined);
+	});
+
+	it("should return an object with the right prototype", function () {
+		var iter = new TestIterator([]).chunks(1);
+		// use `Iterator.prototype.take` as a way to get `IteratorHelperPrototype`
+		proclaim.isFunction(iter.take);
+		proclaim.equal(Object.getPrototypeOf(iter), Object.getPrototypeOf(iter.take(0)));
+	});
+});
diff --git a/polyfills/Iterator/prototype/includes/config.toml b/polyfills/Iterator/prototype/includes/config.toml
new file mode 100644
index 000000000..71e2977cc
--- /dev/null
+++ b/polyfills/Iterator/prototype/includes/config.toml
@@ -0,0 +1,32 @@
+aliases = [ "es2027" ]
+dependencies = [
+	"_ESAbstract.CreateMethodProperty",
+	"_ESAbstract.Get",
+	"_ESAbstract.IsInteger",
+	"_ESAbstract.IteratorClose",
+	"_ESAbstract.IteratorStepValue",
+	"_ESAbstract.NormalCompletion",
+	"_ESAbstract.SameValueZero",
+	"_ESAbstract.ThrowCompletion",
+	"_ESAbstract.Type",
+	"Iterator",
+	"Number.MAX_SAFE_INTEGER",
+]
+spec = "https://tc39.es/ecma262/#sec-iterator.prototype.includes"
+docs = "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator/includes"
+
+[browsers]
+android = "*"
+bb = "*"
+chrome = "<154"
+edge = "*"
+edge_mob = "*"
+firefox = "<154"
+firefox_mob = "<154"
+ie = "*"
+ie_mob = "*"
+opera = "<138"
+op_mob = "<103"
+safari = "*"
+ios_saf = "*"
+samsung_mob = "*"
diff --git a/polyfills/Iterator/prototype/includes/detect.js b/polyfills/Iterator/prototype/includes/detect.js
new file mode 100644
index 000000000..f5159075c
--- /dev/null
+++ b/polyfills/Iterator/prototype/includes/detect.js
@@ -0,0 +1 @@
+"Iterator" in self && "includes" in self.Iterator.prototype;
diff --git a/polyfills/Iterator/prototype/includes/polyfill.js b/polyfills/Iterator/prototype/includes/polyfill.js
new file mode 100644
index 000000000..86db44094
--- /dev/null
+++ b/polyfills/Iterator/prototype/includes/polyfill.js
@@ -0,0 +1,75 @@
+/* global CreateMethodProperty, Get, IsInteger, Iterator, IteratorClose, IteratorStepValue, NormalCompletion, SameValueZero, ThrowCompletion, Type */
+// 27.1.3.3.9 Iterator.prototype.includes ( searchElement [ , skippedElements ] )
+CreateMethodProperty(Iterator.prototype, "includes", function includes(searchElement /* , skippedElements */) {
+	// 1. Let obj be the this value.
+	var obj = this;
+	// 2. If obj is not an Object, throw a TypeError exception.
+	if (Type(obj) !== "object") {
+		throw new TypeError("`this` is not an object");
+	}
+	// 3. Let iterated be the Iterator Record { [[Iterator]]: obj, [[NextMethod]]: undefined, [[Done]]: false }.
+	var iterated = {
+		"[[Iterator]]": obj,
+		"[[NextMethod]]": undefined,
+		"[[Done]]": false
+	};
+	// 4. If skippedElements is undefined, then
+	var skippedElements = arguments[1];
+	if (skippedElements === undefined) {
+		// a. Let toSkip be +0𝔽.
+		var toSkip = 0;
+	}
+	// 5. Else,
+	else {
+		// a. If skippedElements is not one of +∞𝔽, -∞𝔽, or an integral Number, then
+		if (skippedElements !== Infinity && skippedElements !== -Infinity && !IsInteger(skippedElements)) {
+			// i. Let error be ThrowCompletion(a newly created TypeError object).
+			var error = ThrowCompletion(new TypeError("`skippedElements` is not an integer"));
+			// ii. Return ? IteratorClose(iterated, error).
+			return IteratorClose(iterated, error);
+		}
+		// b. Let toSkip be skippedElements.
+		toSkip = skippedElements;
+	}
+	// 6. If toSkip < -0𝔽, then
+	if (toSkip < 0) {
+		// a. Let error be ThrowCompletion(a newly created RangeError object).
+		error = ThrowCompletion(new RangeError("`skippedElements` is negative"));
+		// b. Return ? IteratorClose(iterated, error).
+		return IteratorClose(iterated, error);
+	}
+	// 7. If toSkip is finite and toSkip > 𝔽(2**53 - 1), then
+	if (toSkip !== Infinity && toSkip > Number.MAX_SAFE_INTEGER) {
+		// a. Let error be ThrowCompletion(a newly created RangeError object).
+		error = ThrowCompletion(new RangeError("`skippedElements` is greater than MAX_SAFE_INTEGER"));
+		// b. Return ? IteratorClose(iterated, error).
+		return IteratorClose(iterated, error);
+	}
+	// 8. Let skipped be +0𝔽.
+	var skipped = 0;
+	// 9. Set iterated to ? GetIteratorDirect(obj).
+	iterated = {
+		"[[Iterator]]": obj,
+		"[[NextMethod]]": Get(obj, "next"),
+		"[[Done]]": false
+	};
+	// 10. Repeat,
+	while (true) {
+		// a. Let value be ? IteratorStepValue(iterated).
+		var value = IteratorStepValue(iterated);
+		// b. If value is DONE, return false.
+		if (value === IteratorStepValue.DONE) {
+			return false;
+		}
+		// c. If skipped < toSkip, then
+		if (skipped < toSkip) {
+			// i. Set skipped to skipped + 1𝔽.
+			skipped++;
+		}
+		// d. Else if SameValueZero(value, searchElement) is true, then
+		else if (SameValueZero(value, searchElement) === true) {
+			// i. Return ? IteratorClose(iterated, NormalCompletion(true)).
+			return IteratorClose(iterated, NormalCompletion(true));
+		}
+	}
+});
diff --git a/polyfills/Iterator/prototype/includes/polyfill.test.js b/polyfills/Iterator/prototype/includes/polyfill.test.js
new file mode 100644
index 000000000..f92077f10
--- /dev/null
+++ b/polyfills/Iterator/prototype/includes/polyfill.test.js
@@ -0,0 +1,54 @@
+/* global Iterator */
+
+it("is a function", function () {
+	proclaim.isFunction(Iterator.prototype.includes);
+});
+
+it("has correct arity", function () {
+	proclaim.arity(Iterator.prototype.includes, 1);
+});
+
+it("has correct name", function () {
+	proclaim.hasName(Iterator.prototype.includes, "includes");
+});
+
+it("is not enumerable", function () {
+	proclaim.isNotEnumerable(Iterator.prototype, "includes");
+});
+
+describe("includes", function () {
+	function TestIterator(arr) {
+		var i = -1;
+		this.next = function () {
+			i++;
+			return { value: arr[i], done: i >= arr.length };
+		};
+	}
+	TestIterator.prototype = Iterator.prototype;
+
+	it("should check whether an iterator includes an element", function () {
+		proclaim.isTrue(new TestIterator(["a", "b", "c"]).includes("a"));
+		proclaim.isTrue(new TestIterator(["a", "b", "c"]).includes("b", 1));
+		proclaim.isFalse(new TestIterator(["a", "b", "c"]).includes("d"));
+		proclaim.isFalse(new TestIterator(["a", "b", "c"]).includes("b", 2));
+		proclaim.isFalse(new TestIterator(["a", "b", "c"]).includes("b", Infinity));
+	});
+
+	it("should throw for invalid `skippedElements`", function () {
+		proclaim.throws(function () {
+			new TestIterator(["a", "b", "c"]).includes("a", NaN);
+		}, TypeError);
+		proclaim.throws(function () {
+			new TestIterator(["a", "b", "c"]).includes("a", -1);
+		}, RangeError);
+		proclaim.throws(function () {
+			new TestIterator(["a", "b", "c"]).includes("a", -Infinity);
+		}, RangeError);
+		proclaim.throws(function () {
+			new TestIterator(["a", "b", "c"]).includes("a", .5);
+		}, TypeError);
+		proclaim.throws(function () {
+			new TestIterator(["a", "b", "c"]).includes("a", Number.MAX_SAFE_INTEGER + 1);
+		}, RangeError);
+	});
+});
diff --git a/polyfills/Iterator/prototype/join/config.toml b/polyfills/Iterator/prototype/join/config.toml
new file mode 100644
index 000000000..56f18101a
--- /dev/null
+++ b/polyfills/Iterator/prototype/join/config.toml
@@ -0,0 +1,29 @@
+aliases = [ "es2027" ]
+dependencies = [
+	"_ESAbstract.CreateMethodProperty",
+	"_ESAbstract.Get",
+	"_ESAbstract.IteratorClose",
+	"_ESAbstract.IteratorStepValue",
+	"_ESAbstract.ThrowCompletion",
+	"_ESAbstract.ToString",
+	"_ESAbstract.Type",
+	"Iterator",
+]
+spec = "https://tc39.es/ecma262/#sec-iterator.prototype.join"
+docs = "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator/join"
+
+[browsers]
+android = "*"
+bb = "*"
+chrome = "<153"
+edge = "*"
+edge_mob = "*"
+firefox = "<154"
+firefox_mob = "<154"
+ie = "*"
+ie_mob = "*"
+opera = "<137"
+op_mob = "<103"
+safari = "*"
+ios_saf = "*"
+samsung_mob = "*"
diff --git a/polyfills/Iterator/prototype/join/detect.js b/polyfills/Iterator/prototype/join/detect.js
new file mode 100644
index 000000000..51b075f68
--- /dev/null
+++ b/polyfills/Iterator/prototype/join/detect.js
@@ -0,0 +1 @@
+"Iterator" in self && "join" in self.Iterator.prototype;
diff --git a/polyfills/Iterator/prototype/join/polyfill.js b/polyfills/Iterator/prototype/join/polyfill.js
new file mode 100644
index 000000000..d4caf1fb9
--- /dev/null
+++ b/polyfills/Iterator/prototype/join/polyfill.js
@@ -0,0 +1,74 @@
+/* global CreateMethodProperty, Get, Iterator, IteratorClose, IteratorStepValue, ThrowCompletion, ToString, Type */
+// 27.1.3.3.10 Iterator.prototype.join ( separator )
+CreateMethodProperty(Iterator.prototype, "join", function join(separator) {
+	// 1. Let obj be the this value.
+	var obj = this;
+	// 2. If obj is not an Object, throw a TypeError exception.
+	if (Type(obj) !== "object") {
+		throw new TypeError("`this` is not an object");
+	}
+	// 3. Let iterated be the Iterator Record { [[Iterator]]: obj, [[NextMethod]]: undefined, [[Done]]: false }.
+	var iterated = {
+		"[[Iterator]]": obj,
+		"[[NextMethod]]": undefined,
+		"[[Done]]": false
+	};
+	// 4. If separator is undefined, then
+	if (separator === undefined) {
+		// a. Let separatorString be ",".
+		var separatorString = ",";
+	}
+	// 5. Else,
+	else {
+		// a. Let separatorString be Completion(ToString(separator)).
+		try {
+			separatorString = ToString(separator);
+		}
+		// b. IfAbruptCloseIterator(separatorString, iterated).
+		catch (error) {
+			return IteratorClose(iterated, ThrowCompletion(error));
+		}
+	}
+	// 6. Set iterated to ? GetIteratorDirect(obj).
+	iterated = {
+		"[[Iterator]]": obj,
+		"[[NextMethod]]": Get(obj, "next"),
+		"[[Done]]": false
+	};
+	// 7. Let result be the empty String.
+	var result = "";
+	// 8. Let first be true.
+	var first = true;
+	// 9. Repeat,
+	while (true) {
+		// a. Let value be ? IteratorStepValue(iterated).
+		var value = IteratorStepValue(iterated);
+		// b. If value is DONE, return result.
+		if (value === IteratorStepValue.DONE) {
+			return result;
+		}
+		// c. If first is true, then
+		if (first === true) {
+			// i. Set first to false.
+			first = false;
+		}
+		// d. Else,
+		else {
+			// i. Set result to the string-concatenation of result and separatorString.
+			result += separatorString;
+		}
+		// e. If value is neither undefined nor null, then
+		if (value !== undefined && value !== null) {
+			// i. Let valueString be Completion(ToString(value)).
+			try {
+				var valueString = ToString(value);
+			}
+			// ii. IfAbruptCloseIterator(valueString, iterated).
+			catch (error) {
+				return IteratorClose(iterated, ThrowCompletion(error));
+			}
+			// iii. Set result to the string-concatenation of result and valueString.
+			result += valueString;
+		}
+	}
+});
diff --git a/polyfills/Iterator/prototype/join/polyfill.test.js b/polyfills/Iterator/prototype/join/polyfill.test.js
new file mode 100644
index 000000000..cc1791b8b
--- /dev/null
+++ b/polyfills/Iterator/prototype/join/polyfill.test.js
@@ -0,0 +1,49 @@
+/* global Iterator */
+
+it("is a function", function () {
+	proclaim.isFunction(Iterator.prototype.join);
+});
+
+it("has correct arity", function () {
+	proclaim.arity(Iterator.prototype.join, 1);
+});
+
+it("has correct name", function () {
+	proclaim.hasName(Iterator.prototype.join, "join");
+});
+
+it("is not enumerable", function () {
+	proclaim.isNotEnumerable(Iterator.prototype, "join");
+});
+
+describe("join", function () {
+	function TestIterator(arr) {
+		var i = -1;
+		this.next = function () {
+			i++;
+			return { value: arr[i], done: i >= arr.length };
+		};
+	}
+	TestIterator.prototype = Iterator.prototype;
+
+	it("should join elements of an iterator", function () {
+		proclaim.equal(new TestIterator(["a", "b", "c"]).join(), "a,b,c");
+		proclaim.equal(new TestIterator(["a", "b", "c"]).join("."), "a.b.c");
+	});
+
+	if ("Symbol" in self) {
+		var sym = self.Symbol("test");
+
+		it("should throw for a symbol element", function () {
+			proclaim.throws(function () {
+				new TestIterator([sym]).join();
+			}, TypeError);
+		});
+
+		it("should throw for a symbol separator", function () {
+			proclaim.throws(function () {
+				new TestIterator([]).join(sym);
+			}, TypeError);
+		});
+	}
+});
diff --git a/polyfills/Iterator/prototype/windows/config.toml b/polyfills/Iterator/prototype/windows/config.toml
new file mode 100644
index 000000000..f26654faf
--- /dev/null
+++ b/polyfills/Iterator/prototype/windows/config.toml
@@ -0,0 +1,33 @@
+aliases = [ "es2027" ]
+dependencies = [
+	"_ESAbstract.CreateIterResultObject",
+	"_ESAbstract.CreateMethodProperty",
+	"_ESAbstract.Get",
+	"_ESAbstract.IsInteger",
+	"_ESAbstract.IteratorClose",
+	"_ESAbstract.IteratorStepValue",
+	"_ESAbstract.NormalCompletion",
+	"_ESAbstract.ThrowCompletion",
+	"_ESAbstract.Type",
+	"Iterator",
+	"Iterator.prototype.take",
+	"Symbol.iterator",
+]
+spec = "https://tc39.es/ecma262/#sec-iterator.prototype.windows"
+docs = "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator/windows"
+
+[browsers]
+android = "*"
+bb = "*"
+chrome = "*"
+edge = "*"
+edge_mob = "*"
+firefox = "<154"
+firefox_mob = "<154"
+ie = "*"
+ie_mob = "*"
+opera = "*"
+op_mob = "*"
+safari = "*"
+ios_saf = "*"
+samsung_mob = "*"
diff --git a/polyfills/Iterator/prototype/windows/detect.js b/polyfills/Iterator/prototype/windows/detect.js
new file mode 100644
index 000000000..f3c0cd88b
--- /dev/null
+++ b/polyfills/Iterator/prototype/windows/detect.js
@@ -0,0 +1 @@
+"Iterator" in self && "windows" in self.Iterator.prototype;
diff --git a/polyfills/Iterator/prototype/windows/polyfill.js b/polyfills/Iterator/prototype/windows/polyfill.js
new file mode 100644
index 000000000..4dd626c3d
--- /dev/null
+++ b/polyfills/Iterator/prototype/windows/polyfill.js
@@ -0,0 +1,130 @@
+/* global CreateIterResultObject, CreateMethodProperty, Get, IsInteger, Iterator, IteratorClose, IteratorStepValue, NormalCompletion, Symbol, ThrowCompletion, Type */
+
+var IteratorHelperPrototype = (function () {
+	var iterator = Object.create(Iterator.prototype);
+	iterator[Symbol.iterator] = function () {
+		return {
+			next: function () {
+				return { value: undefined, done: true };
+			}
+		};
+	};
+	// use `Iterator.prototype.take` as a way to get `IteratorHelperPrototype`
+	var iteratorHelper = iterator.take(0);
+	return Object.getPrototypeOf(iteratorHelper);
+})();
+
+// 27.1.3.3.16 Iterator.prototype.windows ( windowSize [ , undersized ] )
+CreateMethodProperty(Iterator.prototype, "windows", function windows(windowSize /* , undersized */) {
+	// 1. Let obj be the this value.
+	var obj = this;
+	// 2. If obj is not an Object, throw a TypeError exception.
+	if (Type(obj) !== "object") {
+		throw new TypeError("`this` is not an object");
+	}
+	// 3. Let iterated be the Iterator Record { [[Iterator]]: obj, [[NextMethod]]: undefined, [[Done]]: false }.
+	var iterated = {
+		"[[Iterator]]": obj,
+		"[[NextMethod]]": undefined,
+		"[[Done]]": false
+	};
+	// 4. If windowSize is not an integral Number, then
+	if (!IsInteger(windowSize)) {
+		// a. Let error be ThrowCompletion(a newly created TypeError object).
+		var error = ThrowCompletion(new TypeError("`windowSize` is not an integer"));
+		// b. Return ? IteratorClose(iterated, error).
+		return IteratorClose(iterated, error);
+	}
+	// 5. If windowSize is not in the inclusive interval from 1𝔽 to 𝔽(2**32 - 1), then
+	if (windowSize < 1 || windowSize > Math.pow(2, 32) - 1) {
+		// a. Let error be ThrowCompletion(a newly created RangeError object).
+		error = ThrowCompletion(new RangeError("`windowSize` is invalid"));
+		// b. Return ? IteratorClose(iterated, error).
+		return IteratorClose(iterated, error);
+	}
+	// 6. If undersized is undefined, set undersized to "only-full".
+	var undersized = arguments[1];
+	if (undersized === undefined) {
+		undersized = "only-full";
+	}
+	// 7. If undersized is neither "only-full" nor "allow-partial", then
+	if (undersized !== "only-full" && undersized !== "allow-partial") {
+		// a. Let error be ThrowCompletion(a newly created TypeError object).
+		error = ThrowCompletion(new TypeError("`undersized` is invalid"))
+		// b. Return ? IteratorClose(iterated, error).
+		return IteratorClose(iterated, error);
+	}
+
+	// 8. Set iterated to ? GetIteratorDirect(obj).
+	iterated = {
+		"[[Iterator]]": obj,
+		"[[NextMethod]]": Get(obj, "next"),
+		"[[Done]]": false
+	};
+	// 9. Let closure be a new Abstract Closure with no parameters that captures iterated, windowSize, and undersized and performs the following steps when called:
+	// 10. Let result be CreateIteratorFromClosure(closure, "Iterator Helper", %IteratorHelperPrototype%, « [[UnderlyingIterators]] »).
+	var result = Object.create(IteratorHelperPrototype);
+	result["[[Done]]"] = false;
+
+	// a. Let buffer be a new empty List.
+	var buffer = [];
+
+	CreateMethodProperty(result, "next", function () {
+		if (this["[[Done]]"] === true) {
+			return CreateIterResultObject(undefined, true);
+		}
+
+		// b. Repeat,
+		while (true) {
+			// i. Let value be ? IteratorStepValue(iterated).
+			try {
+				var value = IteratorStepValue(iterated);
+			} catch (_error) {
+				this["[[Done]]"] = true;
+				throw _error;
+			}
+			// ii. If value is DONE, then
+			if (value === IteratorStepValue.DONE) {
+				this["[[Done]]"] = true;
+				// 1. If undersized is "allow-partial", buffer is not empty, and the number of elements in buffer < ℝ(windowSize), then
+				if (undersized === "allow-partial" && buffer.length > 0 && buffer.length < windowSize) {
+					// a. Perform Completion(Yield(CreateArrayFromList(buffer))).
+					return CreateIterResultObject(buffer.slice(), true);
+				}
+				// 2. Return ReturnCompletion(undefined).
+				return CreateIterResultObject(undefined, true);
+			}
+			// iii. If the number of elements in buffer is ℝ(windowSize), then
+			if (buffer.length === windowSize) {
+				// 1. Remove the first element from buffer.
+				buffer.shift();
+			}
+			// iv. Append value to buffer.
+			buffer.push(value);
+			// v. If the number of elements in buffer is ℝ(windowSize), then
+			if (buffer.length === windowSize) {
+				// 1. Let completion be Completion(Yield(CreateArrayFromList(buffer))).
+				try {
+					return CreateIterResultObject(buffer.slice(), false);
+				}
+				// 2. IfAbruptCloseIterator(completion, iterated).
+				catch (err) {
+					this["[[Done]]"] = true;
+					return IteratorClose(iterated, ThrowCompletion(err));
+				}
+			}
+		}
+	});
+
+	CreateMethodProperty(result, "return", function (value) {
+		if (this["[[Done]]"] !== true) {
+			IteratorClose(iterated, NormalCompletion(value));
+			this["[[Done]]"] = true;
+		}
+		return CreateIterResultObject(undefined, true);
+	});
+
+	// 11. Set result.[[UnderlyingIterators]] to « iterated ».
+	// 12. Return result.
+	return result;
+});
diff --git a/polyfills/Iterator/prototype/windows/polyfill.test.js b/polyfills/Iterator/prototype/windows/polyfill.test.js
new file mode 100644
index 000000000..2bf6d0d48
--- /dev/null
+++ b/polyfills/Iterator/prototype/windows/polyfill.test.js
@@ -0,0 +1,83 @@
+/* global Iterator */
+
+it("is a function", function () {
+	proclaim.isFunction(Iterator.prototype.windows);
+});
+
+it("has correct arity", function () {
+	proclaim.arity(Iterator.prototype.windows, 1);
+});
+
+it("has correct name", function () {
+	proclaim.hasName(Iterator.prototype.windows, "windows");
+});
+
+it("is not enumerable", function () {
+	proclaim.isNotEnumerable(Iterator.prototype, "windows");
+});
+
+describe("windows", function () {
+	function TestIterator(arr) {
+		var i = -1;
+		this.next = function () {
+			i++;
+			if (arr[i] === "error") {
+				throw new Error("uh oh");
+			}
+			return { value: arr[i], done: i >= arr.length };
+		};
+	}
+	TestIterator.prototype = Iterator.prototype;
+
+	it("should window an iterator", function () {
+		var iter = new TestIterator([1, 2, 3]).windows(2);
+		proclaim.deepStrictEqual(iter.next().value, [1, 2]);
+		proclaim.deepStrictEqual(iter.next().value, [2, 3]);
+		proclaim.equal(iter.next().value, undefined);
+
+		iter = new TestIterator([1, 2, 3]).windows(4);
+		proclaim.equal(iter.next().value, undefined);
+
+		iter = new TestIterator([1, 2, 3]).windows(4, "allow-partial");
+		proclaim.deepStrictEqual(iter.next().value, [1, 2, 3]);
+		proclaim.equal(iter.next().value, undefined);
+	});
+
+	it("should throw for invalid `windowSize`", function () {
+		proclaim.throws(function () {
+			new TestIterator([1, 2, 3]).windows(NaN);
+		}, TypeError);
+		proclaim.throws(function () {
+			new TestIterator([1, 2, 3]).windows(1.5);
+		}, TypeError);
+		proclaim.throws(function () {
+			new TestIterator([1, 2, 3]).windows(0);
+		}, RangeError);
+		proclaim.throws(function () {
+			new TestIterator([1, 2, 3]).windows(Math.pow(2, 32));
+		}, RangeError);
+	});
+
+	it("should throw for invalid `undersized`", function () {
+		proclaim.throws(function () {
+			new TestIterator([1, 2, 3]).windows(1, "oops");
+		}, TypeError);
+	});
+
+	it("should handle errors during iteration", function () {
+		var iter = new TestIterator([1, 2, "error", 4]).windows(1);
+		proclaim.deepStrictEqual(iter.next().value, [1]);
+		proclaim.deepStrictEqual(iter.next().value, [2]);
+		proclaim.throws(function () {
+			iter.next();
+		}, Error);
+		proclaim.equal(iter.next().value, undefined);
+	});
+
+	it("should return an object with the right prototype", function () {
+		var iter = new TestIterator([]).windows(1);
+		// use `Iterator.prototype.take` as a way to get `IteratorHelperPrototype`
+		proclaim.isFunction(iter.take);
+		proclaim.equal(Object.getPrototypeOf(iter), Object.getPrototypeOf(iter.take(0)));
+	});
+});