In Optimality Theory, phonological patterns are accounted for with output constraints ranked in a hierarchy. There is little explanatory role for a theory of operations, and hence little has been said about the Gen component. This situation has changed with the emergence of a derivational version of Optimality Theory called Harmonic Serialism. One of the principal differences between Harmonic Serialism and standard Optimality Theory is that Harmonic Serialism's Gen is limited to doing one thing at a time. Harmonic Serialism's analyses and explanations depend on knowing what it means to “do one thing at a time”, and that requires a precise theory of Gen. This article explains Gen's role in Harmonic Serialism and describes two techniques for discovering properties of Gen.