In January 2004, Congress established the Millennium Challenge Corporation (MCC) to administer the Millennium Challenge Account. MCC's mission is to promote economic growth and reduce extreme poverty in developing countries. The act requires MCC to rely to the maximum extent possible on quantitative criteria in determining countries' eligibility for assistance. MCC will provide assistance primarily through compacts--agreements with country governments. MCC aims to be one of the top donors in countries with which it signs compacts. For fiscal years 2004 and 2005, Congress appropriated nearly $2.5 billion for the Millennium Challenge Corporation; for fiscal year 2006, the President is requesting $3 billion. GAO was asked to monitor MCC's (1) process for determining country eligibility, (2) progress in developing compacts, (3) coordination with key stakeholders, and (4) establishment of management structures and accountability mechanisms. For fiscal years 2004 and 2005, the MCC board used the quantitative criteria as well as judgment in determining 17 countries to be eligible for MCA compacts. Although MCC chose the indicators based in part on their public availability, our analysis showed that not all of the source data for the indicators were readily accessible. In addition, we found that reliance on the indicators carried certain inherent limitations, such as measurement uncertainty. Between August 2004 and March 2005, MCC received compact proposals, concept papers, or both, from 16 eligible countries. It signed a compact with Madagascar in April 2005 and is negotiating compacts with four countries. MCC's 4-year compact with Madagascar for $110 million would make it the country's fifth largest donor. MCC is continuing to refine its compact development process. In addition, MCC has identified elements of program implementation and fiscal accountability that can be adapted to eligible countries' compact objectives and institutional capacities. MCC is taking steps to coordinate with key stakeholders to use existing expertise and conduct outreach. The U.S. agencies on the MCC Board of Directors--USAID, the Departments of State and Treasury, and the Office of the U.S. Trade Representative--have provided resources and other assistance to MCC, and five U.S. agencies have agreed to provide technical assistance. Bilateral and multilateral donors are providing information and expertise. MCC is also consulting with nongovernmental organizations in the United States and abroad as part of its outreach activities. MCC has made progress in developing key administrative infrastructures that support its mission and operations. MCC has also made progress in establishing corporatewide structures for accountability, governance, internal control, and human capital management, including establishing an audit capability through its Inspector General, adopting bylaws, providing ethics training to employees, and expanding its permanent full-time staff. However, MCC has not yet completed comprehensive plans, strategies, and related time frames for establishing these essential management structures and accountability mechanisms on a corporatewide basis. [ABSTRACT FROM AUTHOR]