Transcranial magnetic stimulation (TMS) is a new method, developed nearly 20 years ago, that allows the study of cortical excitability. The whole brain undergoes profound changes in sleep. Motor evoked potentials (MEPs) have been used to trace the effects of sleep on cortical excitability and to the corticomotoneuron connections. Although in the past some technical aspects limited the application of TMS in sleep, recently we observed a new explosion of interest in this field. The main body of data was gathered on sleep physiology, but its diseases or syndromes were also studied in detail. Many single and paired pulse-TMS variables were applied. Moreover, TMS variables were investigated as a potential tool for the diagnosis or the differential diagnosis of sleep disorders. In the recent years, the advent of repetitive TMS offered some therapeutic perspectives, which are under current investigation in few of these disorders. Combining repetitive TMS with electroencephalogram (EEG) represents a new and probably useful approach to sleep. Among the main entities classified in the sleep disease group, the following were subject to TMS studies: obstructive sleep apnoea syndrome (OSAS), propriospinal myoclonus, restless legs syndrome (RLS) with periodic limb movement and narcolepsy. For each of these, we examine the applications of TMS separately.