This paper investigates the syntax/morphology interface along four dimensions, in a study of English participial allomorphy. The results are developed in terms of the framework of Distributed Morphology. First, it is shown that considerations of syntactic locality play a direct role in morphological spell-out. Second, the manner in which vocabulary insertion proceeds is argued to be divided into distinct cycles of insertion, with potentially different conditions on insertion applying in Root-attached vs. non-Root-attached structural domains. Third, it is argued that the study of syncretisms must appeal to a notion that I call Substantive Identity in defining what it means for morphology to be ‘the same’ across the distinct cycles of insertion. Finally, it is shown that in addition to structural locality, string adjacency is also a factor in morphological realization.