This chapter examines testing and the cognitive mechanism behind it: retrieval practice, how it works, and how it can be used in the classroom. Learning and memory researchers study testing as a way to practice memory and examine what factors improve our memory. Learning and memory researchers who study testing mostly focus on the process of retrieval. Retrieval is the process of rebuilding a memory in order to call information to mind. There are a few things to keep in mind when trying to improve memory and learning for a certain set of information. Retrieval is an active process that changes learning. Retrieval is the single most effective tool for learning that students and teachers have in their arsenal. Most myths and criticisms about tests are referring specifically to multiple-choice exams. While testing is a form of retrieval practice, retrieval practice does not have to be formal assessments.