Between the years 1200 and 1600, economic development in Catholic Europe gained momentum. By the end of this period, per-capita income levels were well above the income levels in all other regions of the world. We relate this unique development to the resurrection of Roman law, the rise of canon law, and the establishment of law as a scholarly and scientific discipline taught in universities. We test two competing hypotheses on the impact of these processes on economic growth in medieval Europe. The first conjecture is that the spread of substantive Roman law was conducive to the rise of commerce and economic growth. The second and competing conjecture is that growth occurred not as a result of the reception of substantive Roman law but because of the rational, scientific, and systemic features of Roman and canon law and the training of jurists in the newly established universities (Verwissenschaftlichung). This gave the law throughout Europe an innovative flexibility, which also influenced merchant law (lex mercatoria), and customary law. Using data on the population of more than 200 European cities as a proxy for per-capita income, we find that an important impact for economic development was not primarily the content of Roman law, but the rise of law faculties in universities and the emergence of a legal method developed by glossators and commentators in their interpretation and systematization of the sources of Roman law (Corpus Juris Civilis, Digests) and canon law. The endeavor to extract general normative conclusions from these sources led to abstraction, methodology, and the rise of law as a scholarly discipline. Wherever law faculties were founded anywhere in Europe, jurists learned new legal concepts and skills that were unknown before and conducive for doing business.