Résumé : This paper presents estimates of the long-term impact of various sources of knowledge (R&D performed by the business sector, the public sector and foreign firms) on multifactor productivity growth of 16 countries from 1980 to 1998. The main results show that the three sources of knowledge are significant determinants of long term productivity growth. Further evidence suggests that several factors determine the extent to which each source of knowledge contributes to productivity growth. These factors are the absorptive capability, the origin of funding, the socio economic objectives of government support, and the type of public institutions that perform R&D.