This paper examines the effects of exclusionary practices on the process of technological change, modeled as a sequence of innovations. The winner of an early innovation may be able to take (possibly costly) actions that effectively exclude its rivals from competition for subsequent innovations. The possibility of exclusion can change the equilibrium time pattern of investments in research from that of the case of no exclusion. Conditions that make such a change most likely are also conditions under which such a change is most likely to reduce the efficiency of the allocation of resources to technological change.