We hope to stimulate more systematic research on all areas of legal integration by making available for free and open use a comprehensive data base on preliminary references in EC law. The Data Set, which has been under construction since 1996, is now online at various websites. The data are not publicly accessible elsewhere. In this article, we provide a brief summary of the data base and its potential uses. We begin by introducing the main features of the Data Set. We then discuss some of the dynamics of legal integration in light of our analyses of the data.