Sleep disturbances commonly are associated with anxiety disorders, in particular generalized anxiety disorder, panic disorder, and posttraumatic stress disorder. Sleep loss may exacerbate and contribute to relapse of these conditions. Core features of panic disorder and posttraumatic stress disorder occur in relation to sleep (sleep panic attacks or re-experiencing nightmares). Investigation of sleep in anxiety disorders provides clues to mechanisms of arousal regulation relevant to insomnia and pathologic anxiety. Established treatments for anxiety disorders and insomnia have many overlapping components; however, optimal sequencing and integration of the approaches remain under-investigated.