Rainwater harvesting has been used throughout history as a water conservation measure, particularly in regions where other water resources are scarce or difficult to access. In recent years, researchers and policy makers have shown renewed interest in water use strategies due to rising water demand, increased interest in conservation (both water and energy), and an increased regulatory emphasis on reducing stormwater runoff volumes and associated pollutant loads. In the last decade, as interest in the practice has grown, numerous state, municipal, and regional agencies have adopted or amended codes and guidelines to encourage responsible and effective rainwater harvesting practices. In addition, researchers from universities and non-government organizations, as well as industry consultants, have published papers and articles addressing a broad range of topics related to the installation, maintenance, costs, and performance of harvest and use systems. A literature review of existing research and policy documents related to rainwater harvesting has been conducted, with particular focus on characterizing the current state of the practice in the areas of: (1) water conservation, (2) stormwater volume and pollutant load reduction, (3) code and administration considerations and (4) cost factors. The purpose of this report is to summarize the existing knowledge base in these four areas, assess factors affecting economic benefits of rainwater harvesting, and identify topics requiring additional research.