Migration is one of those subjects that is difficult to explain to nonbelievers. The goal of migration is to generate an image of the subsurface velocity structure, but in order to migrate, one must first assume a velocity structure. Furthermore, until recently, nobody knew the meaning of the numbers output from migration; they were just numbers that made an image that looked more or less like the input data. The situation is further confused by the many different methods of migration: finite difference, Kirchhoff, F‐K, phase shift, reverse time, dip move out (DMO), and others. It is possible to be an expert at one method of migration and understand almost nothing about the other methods. Migration is thus a kind of first aid: what to do while you wait for the mathematicians to arrive. Even the history of the subject is confused, mostly by the tendency of some petroleum companies to permit publication of research in only two instances: (a) when the are sure it will never work on data or (b) when they think the competition either already knows about it or is about to find out.