|Abstract:||This paper presents an Optimality-Theoretic analysis of Polish alternating vowels, known as yers, in both simple and derived paradigms. It is argued that yer alternations are a particular kind of absolute neutralization expected under Richness of the Base, wherein a marked underlying structure is realized differently in different contexts. Due to their marked status, yers are deleted unless their realization (which involves a feature change) can prevent the creation of a complex coda. In this way, independently motivated constraints on syllable wellformedness drive the alternations, revealing a sensitivity to syllable complexity in a language that otherwise permits complex codas. It is shown that the syllable-based analysis provides an explanation for a systematic gap: yer vowels may occur before the final, but not penultimate, consonant in stems ending in triconsonantal clusters. The paper also proposes a novel variant of Output-Output correspondence to account of the leveling of alternations that occurs in derived paradigms.