Insomnia, defined as trouble falling asleep or staying asleep, is a common problem. Occasional insomnia is experienced by more than a third of American adults, and chronic insomnia is known to effect more than one in ten. This issue reviews epidemiology, evaluation, consequences, psychiatric and medical co-morbidities, and various therapies for insomnia. This comprehensive review of the topic will be a must-read for any physician treating sleep disorders...