This book discusses the phonological consequences of the backness distinction in high vowels. It focuses on a single-phoneme approach which does not recognize the existence of the vowel y. The author demonstrates that the role of y is crucial for the analysis of Polish palatalization. If y is recognized as a separate phoneme, then the processes receive a straightforward account in Lexical Phonology and Optimality Theory, the two frameworks used in the study. On the other hand, the absence of y leads to unwarranted exceptionality and entails an extensive use of diacritics or lexical constraints. The analyses show, however, that the lack of y is empirically unfeasible and requires segment indexation, a solution unheard of in phonology.