It has frequently been observed that languages exhibit a resistance against accidental repetition of morphemes, a phenomenon reminiscent of the Obligatory Contour Principle in phonology. While languages vary in the strategies they exhibit in dealing with accidental repetition of free morphemes, these strategies consistently take the form of filters that mention both phonological and syntactic properties of the relevant structure. The minimal phonological condition is adjacency, but often partial or complete identity of form plays a role as well. The minimal syntactic condition specifies the syntactic category of the elements in question, but often shared features are mentioned as well. Given these characteristics, the conclusion seems warranted that avoidance strategies form part of the PF interface. Moreover, this interface must provide a mapping from morphosyntactic to morphophonological representations of the type assumed in realizational models of grammar. For most cases of haplology involving free forms, a purely syntactic analysis is unsatisfactory, primarily because it cannot express the generalizations that seem to underlie the data. For example, it cannot but treat the relevance of adjacency as an epiphenomenon.