A number of recent research studies have proven the importance of the preproject planning phase of the construction life cycle. Specifically, a complete scope definition improves project performance in the area of cost, schedule, and operational characteristics. The building construction industry, however, has lacked a publicly available tool for determining the adequacy of scope definition during this critical stage of the project. Aiming to develop a generic, user-friendly preproject planning tool, a multi-disciplinary research team at the Construction Industry Institute (CII) has developed a Project Definition Rating Index (PDRI) to address this need. Specifically, the PDRI for buildings is a comprehensive checklist of 64 scope definition elements weighted according to their relative importance and presented in a score sheet format. Similar to an earlier version developed for industrial projects, the PDRI provides a means for an individual or team to evaluate the status of a building project during preproject planning with a score corresponding to its level of definition. This paper will discuss the development process of the PDRI, including the methodology used and how industry input from 69 professionals has been incorporated in weighting each of the 64 elements. Key project scope definition elements will be identified. Also included are a description of the potential uses of the PDRI and a summary of the benefits it will provide to the U.S. building construction industry.