Patent policy, patent pools, and the accumulation of claims in sequential innovation

We present a dynamic model where the accumulation of patents generates an increasing number of claims on sequential innovation. We study the equilibrium innovation activity under three regimes: patents, no-patents and patent pools. Patent pools increase the probability of innovation with respect to patents, but we also find that: (1) their outcome can be replicated by a licensing scheme in which innovators sell complete patent rights, and (2) they are dynamically unstable. We find that none of the above regimes can reach the first or second best. Finally, we consider patents of finite duration and determine the optimal patent length.