I am associate professor of economics at Utrecht University School of Economics, and specialised in game theory and microeconomic theory. A large part of my recent research investigates the circumstances enabling people to undertake collective action or form mutually beneficial networks, such as an outside threat or common enemy. More recently, I investigate whether competition has a dark side in leading to sabotage. Apart from this, I continue to investigate social and economic networks, and competitive mechanisms such as actions. I cooperate with experimental economists to test hypotheses rooted in economic theory. I apply my research mainly to economics, but also make contributions to political science (in particular: government repression) and theoretical biology (in particular: evolutionary game theory).