To truly understand how important and central memory is to us, it is important to understand what life is like for people who experience memory loss, or amnesia. This chapter examines the amnestic syndrome, which has been widely studied and the knowledge of which has significantly influenced theories of memory. The abilities and nonabilities of those with amnestic syndrome demonstrate that there are multiple independent systems of memory. The chapter also examines two controversial diagnoses, the main feature of which is memory loss dissociative identity disorder (DID) and psychogenic or dissociative amnesia. It discusses a form of memory loss that does not fit the technical definition of amnesia because it eventually affects not just memory but all cognition: Alzheimer’s disease (AD). AD is common among older adults and demonstrates how a worsening loss of memory and cognition can lead to a complete disruption of everyday life.