Economic Insight has published an article in Issue 3 of the ThoughtLeaders4Competition magazine. We examine how the formation and frequency of cartels was affected by the European Commission’s 2006 changes to its fine guidelines for cartels, which increased the fines imposed for infringements and provided greater consistency between cases. In particular, the article discusses how industrial economics can be used to predict how firms would respond to these changes, before reviewing the empirical data to test whether the theory aligns to the realised facts.