In this project we are interested in studying the determinants of cooperation. More precisely, we want to see what decides an economic agent to contribute to the team effort. Our experimental design allows us in particular to control for the effects of the performance of one's teammate and her team-spirit. Our preliminary results indicate that our subjects tend to contribute more to the team when they know their teammate will share their team-spirit and that women and subjects who are confident in their relative performance contribute more to the team when their teammate is someone whose performance is close to theirs.