Researchers of women's representation need to explicitly establish the link between descriptive and substantive representation rather than assume that the mere increase in women in politics leads to substantial changes in political outcomes. Collaboration of women in parliaments is one way through which descriptive representation of women translates into substantive representation. I expand the analysis of bill cosponsorship that has been conducted in the United States (e.g. Bratton and Rouse, 2011) and Argentina (Barnes, 2016) to European countries. I use a unique dataset of cosponsorship data scraped from the archives of several European parliaments including Italy, Sweden, Hungary, Belgium and the Czech Republic, taking advantage of the broad range of electoral systems, quota regimes and levels of women’s representation present in these countries. The results show that women are more likely to collaborate with other women in situations when they are marginalised in the legislature, while men begin to collaborate with women at higher levels once women achieve a substantial share of the seats in parliament. Most importantly, the electoral system has a different effect on collaboration for male and female politicians: While men are more likely to collaborate with women in systems featuring single member districts, women are more likely to collaborate with each other in mixed systems. These results show how the institutional setting of a parliament influences the strategies female politicians can use to represent female voters.