Most people's experiences of poor sleep are memorable, because sleeplessness and its daytime consequences are unpleasant. There are those, however, for whom insomnia is the norm. Persistent and severe sleep disturbance affects at least one in 10 adults and one in five older adults, thus representing a considerable public health concern. Sleep disruption is central to a number of medical and psychiatric disorders, and insomnia is usually treated by general practitioners. Therefore differential diagnosis is important, and respiratory physicians, neurologists, psychiatrists, and clinical psychologists need to be involved. The purpose of this chapter is to summarize current understanding of the insomnias, their appraisal, and treatment. Particular emphasis will be placed upon evidence-based practical management.