Institutional change refers to the processes through which formal and informal rules governing social interaction are created, transformed, and replaced over time. Within the perspective of analytical sociology, institutional change is explained by identifying the micro-level mechanisms linking individual beliefs, preferences, and actions to macro-level institutional outcomes. Rather than treating institutions as exogenous or self-reproducing entities, this approach emphasizes how strategic behavior, social influence, learning, coordination, and power relations generate both stability and transformation. The entry reviews key mechanisms of institutional emergence and change, including norm diffusion, collective action, feedback effects, and path dependence. It also discusses how endogenous preference change, network structures, and incentive reconfiguration contribute to gradual adaptation as well as abrupt institutional shifts. By integrating rational choice, network theory, and evolutionary dynamics, analytical sociology offers a mechanism-based framework that bridges structure and agency in the study of institutional change. The entry concludes by highlighting methodological implications for empirical research and the relevance of mechanism-based explanations for comparative and historical institutional analysis.