We consider the optimal taxation of a good which exhibits a negative externality, in a setting where agents differ in their value for the good, their disutility for the externality and their value for money, and the planner observes neither. Pigouvian taxation is the unique Pareto efficient...

We study a model of network externalities transmitted over links wherein the externalities stem from links themselves rather than nodes. For example, bilateral investments can fail and trigger cascading defaults of firms. Joint research projects can succeed and innovations can be diffused over...