This chapter provides a brief introduction to the modern science of memory and presents some significant issues in the field. The contributions of Hermann Ebbinghaus, Frederick Bartlett, and Brenda Milner reveals important insights into how memory works, and the chapter draws upon each approach in characterizing the functional organization of human memory. One of the most significant questions in memory research has been whether there is a fundamental difference between the retention of information across short delays versus long delays. Working memory (WM) model proposes a separation between short-term storage (or maintenance) and the manipulation of information in the service of task goals. Successful memory performance depends not only on how information is encoded, but also on interactions between encoding and retrieval processes. Forgetting can occur even for information that was adequately processed at encoding. Consolidation theory and interference theory are the most popular accounts of forgetting.