The paper is an attempt to trace milestones in the understanding of sputtering by ion bombardment. The field developed rapidly between 1955 and the end of the 1980s, but several important aspects are still under active investigation today. The focus here is on the evolution of the present understanding of the process of sputter emission. The presentation is based primarily on physical arguments, supported by results from theory referred to in the text. Many research groups have contributed to this field. Doing justice to them all appears close to impossible within the given frame. (C) 2012 Elsevier B. V. All rights reserved.