Polysomnographic technology has advanced by exponential degrees since the first sleep studies were conducted by Dement. The basic electrical concepts have remained the same since that time and are an essential element in the understanding of polysomnographic equipment. The application of these basic electrical concepts has allowed, however, for an improvement in the acquisition, manipulation, and storage of physiologic data during sleep. This article defines polysomnography in terms of its history and its current status. The basic electrical concepts are presented with their application to polysomnography. A discussion of other basic principles is included with practical application. © 2005 Elsevier Inc. All rights reserved.