This paper focuses on the properties of the matching process which leads to scientific collaboration. In a first step, it proposes a simple theoretical model to describe the intertemporal choice of researchers facing successive opportunities of co-authoring papers. In a second part, the paper empirically assesses the properties of the model. The main empirical result is that the number and the productivity of a researcher's co-authors reflect the productivity of this researcher. This result is consistent with the assumption that co-authorship is motivated by a willingness to increase both the quality and the quantity of research output. As researchers with a lot of influent publications papers may create links with a large number of influential co-authors, co-authoring with highly productive academics appears as a signaling device of researchers' quality.