There are three types of insomnia disorder: short-term insomnia disorder, chronic insomnia disorder, and other insomnia disorder. Most people with insomnia have the short-term or chronic type. The American Academy of Sleep Medicine publishes the International Classification of Sleep Disorders, which is the leading source of information on categorizing sleep disorders. The third edition of this manual simplified the classification system for insomnia, reducing the number of insomnia subtypes.