During the past decade, significant advances have been made in TeV gamma-ray astronomy arising mainly from development of the imaging atmospheric Cerenkov technique (IACT). This topical review summarizes instrumental and analytical advances which have made possible the rejection of the background hadronic showers with an efficiency close to 100%, while simultaneously rejecting no more than 50% of genuine gamma-ray showers. Application of large optical reflectors to the detection and registration of shower images is described, together with image formation and mapping of Cerenkov photons using high-resolution imaging focal plane detectors. An overview is presented of how images are processed and parametrized, prior to gamma/hadron separation. In the context of rejection strategies, the deleterious muon background is also discussed. The gradual evolution of a number of dedicated gamma/hadron separation strategies is summarized from the standpoint of both single and multiple telescope operation. The review concludes with an overview of astrophysical accomplishments to date, based on successful application of proven gamma hadron separation strategies. Potential future trends are discussed.
