Tonight will see the third of four meetings in quick succession to take place between Real Madrid and Barcelona.
So far, it's honours even. A 1-1 draw in La Liga effectively handed Barcelona the league title while a 1-0 extra-time win saw Real Madrid clinch the Copa del Rey.
Now it's time to decide the Champions League, with the first-leg taking place tonight at the Bernabeu. The usually outwardly confident Jose Mourinho concedes the game is too close to call. "There are no favourites in semi-finals," he said. "Maybe after the first leg we can talk about one team having a slight advantage."
Here, we bring you some of the best ever games between the two sides, find out how El Clasico earned it's reputation and look ahead to the semi-final.
Wednesday 27 April: Champions League semi-final, Bernabeu
Tuesday May 3: Champions League semi-final, Nou Camp