Insomnia is a highly prevalent condition that is known to be associated with important pathophysiological, cognitive, and functional consequences. Adults of all ages and all states of health frequently suffer from insomnia. Therefore, nurses are likely to encounter patients with insomnia in many health care and home settings, including primary care, and acute and long-term care settings. Assessment for insomnia should routinely be incorporated into nursing practice in these settings. Although hypnotics are of some use, cognitive behavioral therapy for insomnia (CBT-I) offers the best long-term results in improving sleep and the daytime sequela resulting from poor sleep. Nurse at all levels play an important role in assessment of insomnia, education about the importance of insomnia, and offering strategies for prevention of chronic insomnia. Effective diagnosis, prevention, and treatment of insomnia are likely to have important effects on reducing its deleterious effects on pathophysiology, functional performance, and quality of life.