In his 1976 Presidential Address to the American Finance Association, Merton Miller provided a compelling argument that there currently exists no viable theory of the optimal capital structure of an individual firm. This argument follows from the critique he presented of existing models of capital structure and from the theory he outlined of the optimal aggregate capital structure of the economy as a whole. That theory depends on the existence of different marginal tax rates for individuals and a tax-free security. Professor Miller pointed out that he was motivated to develop his hypothesis by the apparent inadequacy of a (if not the most) popular explanation for capital structure at both the micro and the aggregate level: the tradeoff between the tax advantages of debt and the cost to the firm's security holders of the bankruptcy process. He observed that neither the tax advantage of debt nor the costs of bankruptcy may be quite what they seem at first glance. When the corporate income tax and the differential taxation of regular income and capital gains are taken into account, then the tax advantage of debt is reduced. Moreover, the limited empirical evidence from actual bankruptcies suggests that the real costs to security holders of bankruptcy may be really rather low. And the recent discussion by Haugen and Senbet [6] suggests that most of the costs attributed to bankruptcy are really costs of liquidation of the firm's assets and not relevant to the capital structure decision.