Harmonic serialism is an active research programme in phonology and syntax but has so far not been pursued in morphology. This book delivers a proof of concept: It shows that harmonic serialism can be substantiated as a viable approach to inflectional morphology, covering roughly the same ground as standard models like Distributed Morphology or Paradigm Function Morphology. Furthermore, based on empirical evidence from a variety of typologically different languages, Inflectional Morphology in Harmonic Serialism offers a fresh perspective on the composition of inflected words that is made possible by a strictly derivational orientation incorporating repeated optimization procedures. This gives rise to new and convincing solutions to some recalcitrant problems in inflectional morphology, related to phenomena like affix order, extended exponence, disjunctive blocking, non-local stem allomorphy, *ABA patterns, impoverishment effects, deponency, and paradigm gaps. The book introduces harmonic serialism from scratch and develops morphological analyses against the background of applications of the theory in phonology and syntax. It will be of use to students and scholars interested in morphology, phonology, syntax, and grammatical theory more generally.