This chapter addresses the age-related changes in sleep and the nature, assessment, diagnosis, and epidemiology of older adults with insomnia (OAWI) from a behavioral sleep medicine perspective. Complaints of insomnia are categorized into difficulty falling asleep, difficulty maintaining sleep, unwanted early morning awakenings, and non-restorative sleep often with daytime consequences such as excessive daytime sleepiness and fatigue. Factors that interfere with the opportunity to obtain sufficient sleep include other sleep disorders, substance use, shift work, or the presence of another psychiatric disorder. As one moves from middle age to the later years of life, the aging process creates changes in sleep architecture and continuity that increase the vulnerability to developing chronic insomnia. Research indicates that some crucial interventions that buffer against chronic insomnia may help the older adult to adopt a regular daily schedule, a healthier lifestyle and sleep behaviors, and increase the quality of social interactions and physical activity.