This thesis investigates the effects football games in major international tournaments have on stock market returns. The major international football tournaments are limited to the FIFA World Cup and the UEFA European Championship, and the games studied are only the finals of these tournaments. The thesis deploys a method of difference in difference with synthetic control groups to capture any effects winning or losing of these games may have on the stock market returns in the following days. The last 22 years of finals in the FIFA World Cup and UEFA European Championship are studied in 11 games and thus 22 treatments. In general, a good fit of the synthetic counterfactuals prior to the event taking place is achieved. The positive and negative events are looked at separately rather than game by game since the distinction between negative and positive events is made by previous literature. All games are treated as equally important since they are all the final of a tournament. The estimated gaps are insignificant for a majority of the games, and no causal relationship between the outcome of finals in international football tournaments and returns on broad stock market indices can be established, possible reasons for this are, among other things, that the indices used in this study is mainly all share indices and large cap indices, which are generally stable.