A key feature of modern dynamic economies is imperfect competition. Some imperfect competition is due to institutions such as patents and copy-rights that allow Þrms to exercise market power over the sale of products they invent. Some imperfect competition is due to various forms of increas-ing returns to scale and product differentiation. Since market power is an essential feature of innovation and growth in the new economy (as it was in the old economy) we need to know how imperfect competition affects the conventional wisdom on tax policy. We argue that it has particularly striking implications for the taxation of capital. The current consensus among economists is that investment should be lightly taxed with most tax revenues coming from labor and consumption taxation; see Kenneth L. Judd (1999) for a discussion of this literature. These analyses assume perfect competition in all markets. Even though imperfect competition is common, economists generally prefer competitive models since analyses with imperfect competition usually get mired in strategic details