We develop a theory of movement operations that occur after the syntactic derivation, in the PF component, within the framework of Distributed Morphology.The theory is an extension of what was called Morphological Merger in Marantz 1984 and subsequent work.A primary result is that the locality properties of a Merger operation are determined by the stage in the derivation at which the operation takes place: specifically, Merger that takes place before Vocabulary Insertion, on hierarchical structures, differs from Merger that takes place post—Vocabulary Insertion/linearization.Specific predictions of the model are tested in numerous case studies.Analyses showing the interaction of syntactic movement, PF movement, and rescue operations are provided as well, including a treatment of English do -support.