In this first book-length study of synchronic umlaut, a comprehensive comparative analysis of the phonology and morphology of the umlaut alternation in present-day German and the Austronesian language Chamorro is presented in the framework of Optimality Theory. Umlaut in German and Chamorro is local and noniterative vowel fronting at the edge of a morphological base. Umlaut in German is stress-insensitive, morphologically conditioned, and takes place at the right edge of words, whereas Chamorro umlaut interacts significantly with stress, is phonologically...