Résumé : The joint increase in the number and size of patents filed around the world puts the patent system under pressure. This paper analyses the sources of this surge in number of claims and pages of patent applications at the EPO. Four hypotheses are scrutinized: the diffusion of national drafting practices, the increasing complexity of inventions, the emergence of new sectors, and new patenting strategies. The results show that the increasing voluminosity is explained by all these hypotheses and suggest that the diffusion of the US model through the PCT is one of the major factors driving the size of EPO patent applications.