Mockito is a popular Java testing framework that allows developers to write tests for mock objects, making it easy to test code that relies on external services or libraries. It provides a set of tools and annotations for creating mock objects, simulating interactions with those objects, and asserting that the results of those interactions match expected behavior. Mockito can be used for a variety of testing scenarios, such as testing REST APIs, testing database interactions, testing network requests, and more. It is known for its flexibility, ease of use, and powerful testing capabilities.