The properties of insulated antennas that make them useful for subsurface communication or heating are discussed. Several antennas and associated feed lines suitable for use in bore holes or for insertion into tissue are analyzed and compared. The nature of lateral waves is reviewed in their relation to the source that generates them. The properties of antennas designed to excite and receive lateral electromagnetic waves are discussed and practical directional antennas and arrays for subsurface communication by means of lateral waves are reviewed.