Assisted living is a prominent and significant component of long-term care for older persons in the United States. This chapter introduces the reader to the assisted living industry. First, it describes the context of long-term care services, needs, and associated costs. Next, it includes the historical evolution of assisted living to help the reader understand the background and development of today’s assisted living communities. Because there is no single nationally accepted definition of assisted living, the chapter provides multiple definitions along with their sources. Then it incorporates a description of common resident characteristics, including resident profiles, length-of-stay averages, reasons residents leave assisted living communities, and common payment sources. The chapter closes with an overview of some of the challenges related to quality of care in assisted living, highlighting the important need for knowledgeable administrators in the industry.