Somnology is the scientific study of sleep. It includes clinical study and treatment of sleep disorders and irregularities. Sleep medicine is a subset of somnology.
Somnologists employ various diagnostic tools to determine the nature of a sleep disorder or irregularity. Some of these tools can be subjective such as the sleep diaries or the sleep questionnaire. Other diagnostic tools are only used while the patient is asleep such as the polysomnograph and actigraphy.
Though somnology does not necessarily mean sleep medicine, somnologists can use behavioral, mechanical, or pharmacological means to correct a sleep disorder.