What is the role of the Advocate General (the AG) in bringing about jurisprudential change? This thesis provides a comprehensive and systematic account of AG influence on doctrinal development in EU competition law. Empirical legal research has dedicated some attention to AG influence by studying how often and to what extent the European Court of Justice (the Court) follows her opinions. The main difficulty of these existing accounts lies in the precise determination of when the Court reached a certain conclusion at the behest of an AG and when it arrived there on its own. Contrary to conventional wisdom, the present thesis examines the impact the AG can have by illuminating her role within the Court – both as an initiator and driver of change. For this purpose, this thesis develops an institutionalist theory of jurisprudential change that fleshes out two distinct modes of change: disruptive and continuous change. These modes are associated with permissive conditions that arise from different combinations of contextual factors. Depending on how specific factors are combined, stronger or weaker incentives for either type of change emerge. This thesis combines quantitative methods with case study evidence to corroborate the hypotheses on which the proposed theory rests. Based on an original dataset containing 263 hand-coded observations, it uses statistical modelling to identify paradigmatic opinions in which the AG opted for change over consolidation. In line with the theory developed, it concludes that disruptive change is more likely in cases where the AG enjoys little discretion, but barriers to change are low. In turn, continuous change is more likely when the AG has a wide margin of discretion, but barriers to change are high. The thesis finds that it is the AG’s role as an actor of change that renders her presence distinct and indispensable for the Court.