Mockito is a popular Java-based framework used for creating mock objects in unit tests. It allows developers to simulate the behavior of complex objects, making it easier to test individual components of an application without relying on their actual implementations. This helps ensure that tests are focused and efficient. By using Mockito, developers can define how mock objects should respond to specific method calls, enabling them to verify interactions and assert expected outcomes. This leads to more reliable tests and helps identify issues early in the development process, ultimately improving code quality and maintainability.