Two decades have passed since the Clean Air Act Amendments of 1990 launched a grand experiment in market-based environmental policy: the SO2 cap-and-trade system. That system performed well but created four striking ironies. First, by creating this system to reduce SO2 emissions to curb acid...

Platform businesses add value by facilitating interactions between customers who are attracted in part by network externalities. Two-sided platform businesses with low costs of reversing participation status have become more important with the rise of the Internet. This essay is concerned with...