In this paper, I provide a unified account of three frequency effects in phonology. First, typologically marked elements are underrepresented. Second, phonological changes are underrepresented. Third, morphologically conditioned phonological changes are overrepresented. These effects are demonstrated with corpus data from English and Welsh. I show how all three effects follow from a simple conception of phonological complexity. Further, I demonstrate how this notion of complexity makes predictions about other phenomena in these languages, and that these predictions are borne out. I model this with traditional Optimality Theory, but the proposal is consistent with any constraint-based formalism that weights constraints in some way.