diff --git a/readme.md b/readme.md
index 76f167d..c9b5463 100644
--- a/readme.md
+++ b/readme.md
@@ -432,6 +432,28 @@ Returns `true` if `value` is an odd integer.
 
 Returns `true` if `value` can be used as an object property key (either `string`, `number`, or `symbol`).
 
+##### .formData(value)
+
+Returns `true` if `value` is an instance of the [`FormData` class](https://developer.mozilla.org/en-US/docs/Web/API/FormData).
+
+```js
+const data = new FormData();
+
+is.formData(data);
+//=> true
+```
+
+##### .urlSearchParams(value)
+
+Returns `true` if `value` is an instance of the [`URLSearchParams` class](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams).
+
+```js
+const searchParams = new URLSearchParams();
+
+is.urlSearchParams(searchParams);
+//=> true
+```
+
 ##### .any(predicate | predicate[], ...values)
 
 Using a single `predicate` argument, returns `true` if **any** of the input `values` returns true in the `predicate`:
diff --git a/source/index.ts b/source/index.ts
index 875794a..86499f1 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -47,6 +47,8 @@ const objectTypeNames = [
 	'DataView',
 	'Promise',
 	'URL',
+	'FormData',
+	'URLSearchParams',
 	'HTMLElement',
 	...typedArrayTypeNames
 ] as const;
@@ -362,6 +364,9 @@ is.nonEmptyMap = <Key = unknown, Value = unknown>(value: unknown): value is Map<
 
 // `PropertyKey` is any value that can be used as an object key (string, number, or symbol)
 is.propertyKey = (value: unknown): value is PropertyKey => is.any([is.string, is.number, is.symbol], value);
+is.formData = (value: unknown): value is FormData => isObjectOfType<FormData>('FormData')(value);
+
+is.urlSearchParams = (value: unknown): value is URLSearchParams => isObjectOfType<URLSearchParams>('URLSearchParams')(value);
 
 export type Predicate = (value: unknown) => boolean;
 
@@ -523,6 +528,8 @@ interface Assert {
 	emptyMap: (value: unknown) => asserts value is Map<never, never>;
 	nonEmptyMap: <Key = unknown, Value = unknown>(value: unknown) => asserts value is Map<Key, Value>;
 	propertyKey: (value: unknown) => asserts value is PropertyKey;
+	formData: (value: unknown) => asserts value is FormData;
+	urlSearchParams: (value: unknown) => asserts value is URLSearchParams;
 
 	// Numbers.
 	evenInteger: (value: number) => asserts value is number;
@@ -621,6 +628,8 @@ export const assert: Assert = {
 	emptyMap: (value: unknown): asserts value is Map<never, never> => assertType(is.emptyMap(value), AssertionTypeDescription.emptyMap, value),
 	nonEmptyMap: <Key = unknown, Value = unknown>(value: unknown): asserts value is Map<Key, Value> => assertType(is.nonEmptyMap(value), AssertionTypeDescription.nonEmptyMap, value),
 	propertyKey: (value: unknown): asserts value is number => assertType(is.propertyKey(value), 'PropertyKey', value),
+	formData: (value: unknown): asserts value is FormData => assertType(is.formData(value), 'FormData', value),
+	urlSearchParams: (value: unknown): asserts value is URLSearchParams => assertType(is.urlSearchParams(value), 'URLSearchParams', value),
 
 	// Numbers.
 	evenInteger: (value: number): asserts value is number => assertType(is.evenInteger(value), AssertionTypeDescription.evenInteger, value),
diff --git a/test/test.ts b/test/test.ts
index 6c2ae57..87455db 100644
--- a/test/test.ts
+++ b/test/test.ts
@@ -1621,6 +1621,48 @@ test('is.all', t => {
 	});
 });
 
+test('is.formData', t => {
+	const data = new window.FormData();
+	t.true(is.formData(data));
+	t.false(is.formData({}));
+	t.false(is.formData(undefined));
+	t.false(is.formData(null));
+
+	t.notThrows(() => {
+		assert.formData(data);
+	});
+	t.throws(() => {
+		assert.formData({});
+	});
+	t.throws(() => {
+		assert.formData(undefined);
+	});
+	t.throws(() => {
+		assert.formData(null);
+	});
+});
+
+test('is.urlSearchParams', t => {
+	const searchParams = new URLSearchParams();
+	t.true(is.urlSearchParams(searchParams));
+	t.false(is.urlSearchParams({}));
+	t.false(is.urlSearchParams(undefined));
+	t.false(is.urlSearchParams(null));
+
+	t.notThrows(() => {
+		assert.urlSearchParams(searchParams);
+	});
+	t.throws(() => {
+		assert.urlSearchParams({});
+	});
+	t.throws(() => {
+		assert.urlSearchParams(undefined);
+	});
+	t.throws(() => {
+		assert.urlSearchParams(null);
+	});
+});
+
 test('assert', t => {
 	// Contrived test showing that TypeScript acknowledges the type assertion in `assert.number()`.
 	// Real--world usage includes asserting user input, but here we use a random number/string generator.