Trade-Off and Pecking Order Theories of Debt**We thank Long Chen, Sudipto Dasgupta, Espen Eckbo, Chris Hennessy, Jay Ritter, Michael Roberts, Tan Wang, and Jaime Zender for comments and helpful discussions. Murray Frank thanks Piper Jaffray for financial support. Vidhan Goyal thanks the Research Grants Council of the Hong Kong Special Administrative Region for financial support (Project No. 6489/06H). The literature on capital structure is vast, containing hundreds of papers, and so we cannot hope to cover it all. Inevitably, we have left out a great deal, much of it very important. As such, we apologize in advance for our inevitable oversights. Even more than usual, it must be stressed that this survey reflects only our views.