It is well known that governmental R&D and private R&D have a complementary relationship. However, no previous study has provided an explanation for why that complementary relationship exists. This paper argues that infratechnology is the critical link between governmental and private R&D and that the observed complementarity is the result of technical complementarity at the production level between funding, infratechnology, and knowledge sharing. A theoretical framework based on this argument is developed and examined empirically for supporting evidence. Evidence of technical complementarity is found as well as evidence that governmental R&D stimulates the sharing of knowledge. © 1991, Taylor & Francis Group, LLC. All rights reserved.