The descriptive analysis shows that there are important differences in the inventive performance of regions in OECD economies, as measured by indicators for one of the key types of intellectual assets (i.e., patents). Inventive performance is concentrated in some regions in continental Europe, in North America and Japan. Highly inventive regions tend to cluster together. This spatial dependence is found to have increased over time. The inventive performance of regions is directly influenced by the availability of human capital and R&D expenditure. Local agglomeration factors (proxied by the density of population) are also found to have a significant impact while some negative effects appear when regions are mainly rural or when they are mainly service-oriented. Cross-country differences point to the importance of national innovation systems which shape the institutional framework within which innovation takes form and diffuses.