Sequence analysis (SA) is the systematic descriptive and causal study of sequences, that is, successions of standard categorical states or events. SA is a unique method for representing, comparing, and clustering sequences; for extracting prototypical sequences; and for mining sequence populations. Its core tool, the optimal matching algorithm, screens and discriminates longitudinal processes according to the nature of events, their duration, and their order. Numerous fields in the social and political sciences deal with sequences including life-course analysis, the sociology of professional careers, political sociology, the study of political regimes, and various geographical or ethnographic practices.The entry firstly defines sequences, provides examples of them, and presents SA’s underlying sociological concepts and objectives. It shows how SA differs from other social scientific methods, especially longitudinal, statistical methods. A brief historical account of the method’s development highlights the original intuition, its standardisation, and the dialectic between unity and diversity of the field. The second section relies on a range of concrete applications to present the main usual steps in SA studies: conceptualisation, data collection and preparation, exploration, calculation of dissimilarities, and postdissimilarity treatments. The third section shows the limitations of the standard approaches, and the available variations and variants, including alternative calculations of dissimilarities, multichannel SA, and prototypical sequences.