The central issue facing renewables in the integrated resource planning process is the appropriate assessment of the value of renewables to utility systems. This includes their impact on both energy and capacity costs (avoided costs), and on emissions and environmental impacts, taking account of the reliability, system characteristics, interactions (in dispatch), seasonality, and other characteristics and costs of the technologies. These are system-specific considerations whose relationships may have some generic implications. In this report, we focus on the reliability contribution of wind electric generating systems, measured as the amount of fossil capacity they can displace while meeting the system reliability criterion. We examine this issue for a case study system at different wind characteristics and penetration, for different years, with different system characteristics, and with different modelling techniques. In an accompanying analysis we also examine the economics of wind electric generation, as well as its emissions and social costs, for the case study system. This report was undertaken for the {open_quotes}Innovative IRP{close_quotes} program of the U.S. Department of Energy, and is based on work by both Union of Concerned Scientists (UCS) and Tellus Institute, including America`s Energy Choices and the UCS Midwest Renewables Project.