In active investment climates where firms sequentially improve each other's products, a patent can terminate either because it expires or because a non-infringing innovation displaces its product in the market. We define the length of time until one of these happens as the effective patent life,...

Patents differ from other forms of intellectual property in that independent invention is not a defence to infringement. We argue that the patent rule is inferior in any industry where the cost of independently inventing a product is not too much less than (no less than half) the inventor's...

A partnership is a coalition that divides its output equally. The authors show that when partnerships can form freely, a stable or "core" pa rtition into partnerships always exists and is generically unique. Wh en people differ in ability, the equal-sharing constraint inefficient ly limits the...

We investigate how liability rules and property rules affect the incentives to invest in research tools. We argue that it is hard to deter infringement under any of the enforcement regimes available. However, counterintuitively, a credible threat of infringement can actually be beneficial to the...

I discuss recent contributions to the theory of group formation and the provision of jointly consumed public goods and services. I highlight the distinction between models of pure group formation, and models where the formation of groups and the sharing of public goods are constrained by a...