Today's explorationist is confronted with a large array of three-dimensional depth imaging options, ranging from a variety of Kirchhoff implementations to a variety of wave-equation implementations. Historically, the choice of a depth migration algorithm was simple: Kirchhoff was the only practical option. This has changed. Advances in computing and clever algorithms have made wave-equation migration an economically feasible alternative. However, so many choices mean that making the right choice of imaging method for a given objective can be a daunting task. In this article we briefly examine the origins of the various imaging methods, describe their relative approximations, and assess their relative merits and applicability.