The objectives of this study are threefold: (1) Estimate the maximum potential conventional hydropower capacity and electricity output which could be developed at existing dams in the United States; (2) Identify the constraints which might hinder or prevent the development of this potential; and (3) Identify the means which could be employed to resolve or relax these constraints and the incentives which might be used to spur the development of this potential. The report is organized into three chapters corresponding to the three objectives plus three appendices. Appendix A contains a detailed description of the method used by the Corps to estimate hydropower potential at existing small dams. Appendix B contains supplemental information on the hydropower potential for each of the 21 major drainage basins in the U.S., Alaska, Hawaii, Puerto Rico, and the Virgin Islands, including a summary of the engineering characteristics of the existing dams in each region. Appendix C contains regional statistics on current competing uses of existing reservoir storage space.