AbstractThis article reviews the analysis of vowel harmony in Optimality Theory. Vowel harmony is a phenomenon in which the vowels in a word or another domain show systematic agreement for some property, such as rounding, backness, height, or ATR quality. Optimality Theory is a framework of generative linguistics in which grammars consist of a hierarchy of constraints on outputs. The treatment of various aspects of harmony systems are discussed, including what drives harmony, directionality and trigger control, opaque and transparent segments, dominant‐recessive patterns, and variation. Data from Turkish, Igbo, Pulaar, Diola Fogny, Finnish, and Hungarian are discussed.