diff --git a/.changeset/great-poems-share.md b/.changeset/great-poems-share.md
new file mode 100644
index 0000000..0ddc5af
--- /dev/null
+++ b/.changeset/great-poems-share.md
@@ -0,0 +1,15 @@
+---
+'@apollo/datasource-rest': major
+---
+
+When passing `params` as an object, parameters with `undefined` values are now skipped, like with `JSON.stringify`. So you can write:
+
+```ts
+getPost(query: string | undefined) {
+  return this.get('post', { params: { query } });
+}
+```
+
+and if `query` is not provided, the `query` parameter will be left off of the URL instead of given the value `undefined`.
+
+As part of this change, we've removed the ability to provide `params` in formats other than this kind of object or as an `URLSearchParams` object. Previously, we allowed every form of input that could be passed to `new URLSearchParams()`. If you were using one of the other forms (like a pre-serialized URL string or an array of two-element arrays), just pass it directly to `new URLSearchParams`; note that the feature of stripping `undefined` values will not occur in this case. For example, you can replace `this.get('post', { params: [['query', query]] })` with `this.get('post', { params: new URLSearchParams([['query', query]]) })`. (`URLSearchParams` is available in Node as a global.)
diff --git a/src/RESTDataSource.ts b/src/RESTDataSource.ts
index 23cdd4f..46a1afb 100644
--- a/src/RESTDataSource.ts
+++ b/src/RESTDataSource.ts
@@ -10,11 +10,16 @@ import type { WithRequired } from '@apollo/utils.withrequired';
 
 type ValueOrPromise<T> = T | Promise<T>;
 
-// URLSearchParams is globally available in Node / coming from @types/node
-type URLSearchParamsInit = ConstructorParameters<typeof URLSearchParams>[0];
-
 export type RequestOptions = FetcherRequestInit & {
-  params?: URLSearchParamsInit;
+  /**
+   * URL search parameters can be provided either as a record object (in which
+   * case keys with `undefined` values are ignored) or as an URLSearchParams
+   * object. If you want to specify a parameter multiple times, use
+   * URLSearchParams with its "array of two-element arrays" constructor form.
+   * (The URLSearchParams object is globally available in Node, and provided to
+   * TypeScript by @types/node.)
+   */
+  params?: Record<string, string | undefined> | URLSearchParams;
   cacheOptions?:
     | CacheOptions
     | ((
@@ -195,6 +200,20 @@ export abstract class RESTDataSource {
     return this.fetch<TResult>(path, { method: 'DELETE', ...request });
   }
 
+  private urlSearchParamsFromRecord(
+    params: Record<string, string | undefined> | undefined,
+  ): URLSearchParams {
+    const usp = new URLSearchParams();
+    if (params) {
+      for (const [name, value] of Object.entries(params)) {
+        if (value !== undefined && value !== null) {
+          usp.set(name, value);
+        }
+      }
+    }
+    return usp;
+  }
+
   private async fetch<TResult>(
     path: string,
     request: DataSourceRequest,
@@ -205,7 +224,7 @@ export abstract class RESTDataSource {
       params:
         request.params instanceof URLSearchParams
           ? request.params
-          : new URLSearchParams(request.params),
+          : this.urlSearchParamsFromRecord(request.params),
       headers: request.headers ?? Object.create(null),
       body: undefined,
     };
@@ -216,7 +235,7 @@ export abstract class RESTDataSource {
 
     const url = await this.resolveURL(path, modifiedRequest);
 
-    // Append params to existing params in the path
+    // Append params from the request to any existing params in the path
     for (const [name, value] of modifiedRequest.params as URLSearchParams) {
       url.searchParams.append(name, value);
     }
diff --git a/src/__tests__/RESTDataSource.test.ts b/src/__tests__/RESTDataSource.test.ts
index 3aef2da..488c392 100644
--- a/src/__tests__/RESTDataSource.test.ts
+++ b/src/__tests__/RESTDataSource.test.ts
@@ -6,6 +6,7 @@ import {
   ForbiddenError,
   RequestOptions,
   RESTDataSource,
+  WillSendRequestOptions,
   // RequestOptions
 } from '../RESTDataSource';
 
@@ -95,7 +96,12 @@ describe('RESTDataSource', () => {
 
         getPostsForUser(
           username: string,
-          params: { filter: string; limit: number; offset: number },
+          params: {
+            filter: string;
+            limit: number;
+            offset: number;
+            optional?: string;
+          },
         ) {
           return this.get('posts', {
             params: {
@@ -103,9 +109,17 @@ describe('RESTDataSource', () => {
               filter: params.filter,
               limit: params.limit.toString(),
               offset: params.offset.toString(),
+              // In the test, this is undefined and should not end up in the URL.
+              optional: params.optional,
             },
           });
         }
+
+        getPostsWithURLSearchParams(username: string) {
+          return this.get('posts2', {
+            params: new URLSearchParams([['username', username]]),
+          });
+        }
       })();
 
       nock(apiUrl)
@@ -118,11 +132,19 @@ describe('RESTDataSource', () => {
         })
         .reply(200);
 
+      nock(apiUrl)
+        .get('/posts2')
+        .query({
+          username: 'beyoncé',
+        })
+        .reply(200);
+
       await dataSource.getPostsForUser('beyoncé', {
         filter: 'jalapeño',
         limit: 10,
         offset: 20,
       });
+      await dataSource.getPostsWithURLSearchParams('beyoncé');
     });
 
     it('allows setting default query string parameters', async () => {
@@ -133,10 +155,8 @@ describe('RESTDataSource', () => {
           super(config);
         }
 
-        override willSendRequest(request: RequestOptions) {
-          const params = new URLSearchParams(request.params);
-          params.set('apiKey', this.token);
-          request.params = params;
+        override willSendRequest(request: WillSendRequestOptions) {
+          request.params.set('apiKey', this.token);
         }
 
         getFoo(id: string) {
@@ -155,7 +175,7 @@ describe('RESTDataSource', () => {
       const dataSource = new (class extends RESTDataSource {
         override baseURL = 'https://api.example.com';
 
-        override willSendRequest(request: RequestOptions) {
+        override willSendRequest(request: WillSendRequestOptions) {
           request.headers = { ...request.headers, credentials: 'include' };
         }
 
@@ -177,7 +197,7 @@ describe('RESTDataSource', () => {
           super(config);
         }
 
-        override willSendRequest(request: RequestOptions) {
+        override willSendRequest(request: WillSendRequestOptions) {
           request.headers = { ...request.headers, authorization: this.token };
         }