Because of the Moon's unique place in the evolution of rocky worlds, it is a prime focus of NASA's space exploration vision. Currently NASA is defining and implementing a series of robotic orbital and landed missions to the Moon as the initial phase of this vision. To realize the benefits of this activity, NASA needs a comprehensive, well-validated, and prioritized set of scientific research objectives. To help establish those objective, NASA asked the NRC to provide guidance on the scientific challenges and opportunities enabled by sustained robotic and human exploration of the Moon during the period 2008-2013+. This interim report, which focuses on science of the Moon, presents a number of scientific themes describing broad scientific goals important for lunar research, discussions of how best to reach these goals, a set of three priority areas that follow from the themes, and recommendations for these priorities and related areas. A final report will follow in the summer of 2007.