Mutation Testing is a software testing technique used to evaluate the quality of test cases. It involves making small changes, or mutations, to a program's code to create slightly altered versions called mutants. The goal is to see if existing test cases can detect these changes, which indicates their effectiveness. If a test case fails when run against a mutant, it means the test is effective at catching errors. However, if the test passes, it suggests that the test may not be thorough enough. This process helps developers improve their test suites and ensure better software quality.