Abstract. We investigate statistically the characteristics, functioning and incidence of pre-emptive patenting, defined as patent filings whose main effect is to hamper the grant of other patents. Patent applications can be used defensively to prevent the grant of exclusive rights over markets and technologies, in order to ensure freedom of operation or keep competitors out of a given technological field. Combining data from examination outcomes and prior art at the European Patent Office, we develop a methodology to identify pre-emptive patent applications. We find evidence of pre-emption associated with patent applications cited as compromising patentability while not being deemed relevant to the state of the art. We also find that, among them, those which are withdrawn have the strongest pre-emptive power. The coincidence of low inventiveness and high pre-emptive impact supports the idea that some of these patents may be strategically designed by their applicants to block patenting by others.