This paper aims at estimating the determinants of co-authorship in economics. More specifically, we test the existence of a potential relationship between the research efficiency of an individual and that of his co-authors (the so called assortative matching hypothesis) using a novel database of French academic scholars. However, individual research productivity should be an endogenous regressor as the quality of an academic's publication will depend somehow on the quality of his co-authors. We have applied the Two Stage Residual Inclusion (2SRI) approach in order to take into account this endogeneity bias. The main empirical result is that the number and the quality of a researcher's co-authors reflect the productivity of that researcher.There is also a significant gender effect: being a woman has no impact on the probability of never collaborating with other economists but it decreases both the quality and the quantity of co-authors. Finally, lifetime cycles are also an important determinant of the co-authorship trend as the social imprinting hypothesis would suggest. So institutional changes occurred in French academia in mid-eighties have had a large impact on individual research productivity.