Sleep research and sleep medicine have grown rapidly over the last thirty years, partly as a result of the discovery that REM (rapid eye movement) sleep coincided with dreaming and partly because of the discovery of sleep apnea (breathing stopping during sleep). Countries vary in how they deal with sleep disorders; in the U.S. sleep medicine is recognised as a field and it is looked after by the National Heart, Lung and Blood Institute; other medical specialities e.g. neurology, pulmonology, psychiatry, may be influential in other countries. The sleep disorders category is broadly divided into sub-categories that deal with the specific sleep disorders as well as the institutions that regulate, diagnose and treat these disorders. Sleep is affected by the brain's biological clock and so is included in this category. Shift-work sleep disorder and jet-lag are well-known problems that reflect the activity of the biological clock. This category consists of some of the major 'omnibus' sites (SleepNet, Brain Information Service, Sleep Medicine and the SleepWell) that can contain just about everything (information, chats, consultations, portals, etc). It also lists smaller, general information sites as well as sites that provide short and concise general sleep disorders information. The Organisations sub-category is packed with information that is more specific to particular sleep disorders. Apart from listing the various centers, the Sleep Centers sub-category is worth visiting as many of these sites provide useful information on sleep disorders. Anyone with health concerns is reminded that it is advisable to discuss their problems with a licensed medical professional.