The aim of the article is to investigate the determinants of patent citations which are reasonably good proxy for the technological value of an invention. The analysis is based on patents granted by the US Patent and Trademark Office (USPTO) to French and British inventors from 1969 to 1998. Our aim is to explain the frequency of citations rather than why a patent may or may not be cited. This is achieved by examining some of the characteristics associated with highly cited patents. The models we estimate predict that a patent that is frequently cited, and therefore a technologically important patent, is a patent that it is quickly cited and more frequently cited by patent from other technological fields. When the patent is cited by patents from other technological fields this tends to indicate that the cited patent is broader.