This paper measures the extent of party polarization in 15 European parliaments through the ebb and flow of legislative collaboration between their members. Drawing extensively on existing studies of legislative cosponsorship networks, we introduce similar data for 19 parliamentary chambers. We then use exponential graph models to measure the influence of factors such as partisanship and reciprocity on the likelihood of cosponsorship. Our results show enough similarities and variations between countries to encourage comparative network approaches of European legislatures.
