Over the last few years there has been a dramatic surge of interest in time-domain electromagnetic (TDEM) methods of exploration. At this moment it seems appropriate to trace the evolution of transient techniques from their early beginnings to the present. Historically, TD techniques have evolved along two parallel paths, transient EM soundings and transient EM prospecting (or inductive TDEM). The first technique is used primarily to delineate layered structures of interest in oil and groundwater exploration. It is also used in delineating zones of high conductivity within the ground, with the expectation that they might be associated with either geothermal or massive sulfide targets. By contrast, transient EM prospecting is primarily used for locating massive sulfide ore deposits at great depths, and its use is associated almost exclusively with the mining industry.--Modified journal abstract.