The aim of this thesis is to investigate cartels and the impact of competition policy from various angles. Chapter 1, joint with Joan-Ramon Borrell, José Manuel Ordóñez-de-Haro and Juan Luis Jiménez, analyzes the relationship between cartel life cycles and business cycles. We analyze the relationship between cartel startups/breakups and economic cycles using a dataset of cartels sanctioned by the European Commission. Results show that cartels are more likely to be formed when the business has evolved positively in the previous months and managers expect prices to decline, but that cartels also tend to breakup when the business has evolved positively. Upturns in ﬁrm-speciﬁc business cycles appear to cause cartel turnovers: existing cartels die while new ones are set up. Chapter 2 aims at obtaining a precise measure of how much ﬁrms beneﬁt from collusion. I evaluate the causal eﬀect of being a cartel member on the revenues and proﬁts of cartelized ﬁrms, using comparable non-collusive ﬁrms as control group. A dataset of discovered cartel cases in Spain from 1990 to 2014 and an alternative dataset of ﬁrms’ balance sheets are used. Results show that ﬁrms increase their revenues, on average, between 19% and 26% due to the collusive agreement, while no signiﬁcant eﬀect is found on proﬁts. Estimations by cartel duration demonstrate that the members of long-lasting cartels not only increase their revenues (29%−50%), but also their proﬁts more than two times. Further analysis shows that cartels that are proﬁtable from the beginning tend to last longer and do not apply for Leniency Programs. Chapter 3, joint with Joan-Ramon Borrell, Juan Luis Jiménez and José Manuel Ordóñezde-Haro, investigates how Leniency Programs destabilize cartels. We study the eﬀect of the Leniency Program on cartel duration, cartel ﬁnes and on the years of investigation using a diﬀerence-in-diﬀerences program evaluation approach. Cartel cases discovered by the European Commission and the Spanish Competition Authority are analyzed. Results show a short-run eﬀect of the Leniency Program: the detected cartels have longer duration than the ones in the control group. In the long-run, the program decreases cartel duration. On the other hand, no signiﬁcant eﬀect is found on ﬁnes, while the duration of the investigation decreases signiﬁcantly around 0.8-1.3 years.