The metaphor of “repertoire” is increasingly used in the study of contention to convey the fact that people act collectively through a limited set of cultural routines. Yet despite its broad adoption, the term is loosely defined and rarely subject to empirical verification. This has led to unfruitful scholarly disputes, with most perspectives assuming that change in repertoires is independent from how actors perform them. Drawing a parallel between the dynamics of repertoire performance and jazz improvisation, I propose a pragmatist (...) definition of repertoires, understood as relational sets of collective practices that become routinized as habit-sets and become a baseline for innovation when actors face puzzling situations. I then provide a theoretical model for analyzing change in contentious repertoires, which relies on the study of the co-constitutive relation between tactical affordances, actors’ strategies and identities, and contexts. I illustrate this model with three secondary cases of unexpected tactical innovation. (shrink)