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This paper estimates the international diffusion of technical knowledge using patent citations. We control for self‐citations and for procedural differences between patent offices using equivalent patents. We find that (1) there are clear biases in patent examination processes that generate citations in the two offices; (2) at the EPO there is a strong localization effect at the country level, and the size is comparable to that found at the USPTO; (3) technological fields have different properties of diffusion in the two patent offices that do not depend on a patent office bias; (4) using EPO data, the US is not the leading country in terms of citations made and received, as occurs at the USPTO.