Political parties learn from successful foreign parties. But does the scope of this crossnational policy diffusion vary with party family? We use a heuristics framework to argue that
party family conditions transnational policy learning when it makes information on the
positions of sister parties more readily available and relevant. Both conditions apply to social
democracy, which, unlike other party families, faced major competitive challenges from the
1970s in the context of exceptionally strong transnational organizations – factors that, as we
contend, uniquely facilitate cross-national policy learning from successful parties within the
family. We analyze parties’ policy positions using spatial methods and find that social
democratic parties are indeed exceptional as they emulate one another across borders more
than other families. These findings have important implications for our understanding of
political representation and of social democratic parties’ election strategies over the last forty
years.
