Research libraries traditionally have focused their efforts on building local collections to support the research needs of their organizations and providing for the discovery and use of resources within these collections. The emergence in recent years of disciplinary and institutional digital repositories presents new challenges for research libraries. One of the most significant challenges will be the need for new types of statistical assessment based on the use of extra-bibliographic facets of the content in these repositories, such as usage data, impact factors, and contextual relationships. This article summarizes the success of U. S. research libraries in creating shared standards for electronic resources statistical assessment and argues that institutional repository implementers must develop similar evaluative metrics. (Contains 1 figure.)