Insomnia is one of the most common complaints seen in medicine. Incidence and prevalence estimates vary slightly depending on the methodology, but commonly cited figures are that approximately one-third of Americans have symptoms of acute or intermittent insomnia, and that approximately 10% have chronic insomnia. Over the past several decades, there have been great strides in understanding the pathophysiology of insomnia as well as documenting the efficacy of pharmacologic and nonpharmacologic treatments. There are now sufficient data to allow for meta-analyses to be conducted in insomnia, which help compare effect sizes across studies. This chapter provides an overview of the development of insomnia, information required to make a diagnosis of insomnia, the various recognized insomnia diagnoses, and the pharmacologic, cognitive, and behavioral treatments available. (more…)