Morphology can be thought of roughly as the study of the structure of the parts of words, including for instance the nature of affixes. At Penn, morphology research spans into the syntax-morphology interface, in particular with a distributed morphology perspective in which morphology is thought to have the same constituent structures as at the level of syntax.

Much of David Embick's work likewise explores the architecture of native-speaker grammars. He has done important work in Distributed Morphology, a new theory of the architecture of morphosyntax which is still developing rapidly. He also investigates the relation between morphology and argument structure, especially the appearance of related verbs (sometimes ostensibly "the same" verbs) in different syntactic structures. In addition, his work explores the relation between hierarchical syntactic structures and the strings which instantiate them, including phonological aspects of the latter that are relevant to syntax. Many of the questions addressed in this research program are architectural in nature, concentrating on the question of whether there are separate lexical and syntactic modes of derivation in the grammar. The idea behind much of this work is to tie detailed case-studies of phenomena from an individual language or languages to broader questions concerning the architecture of grammars.

Rolf Noyer's work spans phonology and morphology. His dissertation was one of the first full expositions of Distributed Morphology, and he continues to work and publish in this frontier area of the field.

Charles Yang is interested in the real-time mechanisms of morphological processing and storage, and the architectural issues of morphology in the grammar. Of specific concerns is the issue of morphological productivity, which cuts deeply across the domains of morphological learning, processing, and change.