This monograph addresses three basic questions regarding the development of word-internal prosodic structure: How much of the phonological structure of early words is regulated by the same constituents and principles that govern the organization of prosodic structure of mature grammar? Why do early words diverge from the adult targets in shape and size? And what is the best way to model developmental changes that occur in prosodic structure? Answers to these questions are explored through the longitudinal analysis of spontaneous production data from child Japanese. The analysis provides new types of evidence and new arguments that the prosodic phonology of young children is largely continuous with that of adults, and that the surface child-adult divergence in word forms and the overall pattern of developmental changes are best explained in terms of ranked violable constraints on the representation of prosodic structure, whose ordering is modified in the course of acquisition.