The Modigliani–Miller theorem (of Franco Modigliani, Merton Miller) forms the basis for modern thinking on capital structure. The basic theorem states that, under a certain market price process (the classical random walk), in the absence of taxes, bankruptcy costs, agency costs, and asymmetric information, and in an efficient market, the value of a firm is unaffected by how that firm is financed. It does not matter if the firm’s capital is raised by issuing stock or selling debt. It does not matter what the firm’s dividend policy is. Therefore, the Modigliani–Miller theorem is also often called the capital structure irrelevance principle.
Modigliani was awarded the 1985 Nobel Prize in Economics for this and other contributions.
Miller was a professor at the University of Chicago when he was awarded the 1990 Nobel Prize in Economics, along with Harry Markowitz and William Sharpe, for their "work in the theory of financial economics," with Miller specifically cited for "fundamental contributions to the theory of corporate finance."