This article analyses R&D cooperation strategies by foreign subsidiaries of MNEs located in South Korea. It differentiates between foreign subsidiaries with no R&D cooperation and those which favour internal or external R&D cooperation. Providing country-specific discussion in the context of South Korea, this enables comparison and contrast of the importance of innovation networks developed by MNE subsidiaries. Using various models, the results show that foreign subsidiaries in South Korea adopt complementary internal and external R&D cooperation strategies. Knowledge sourcing is found to be a key determinant of R&D cooperation, and government policies act as a strong incentive for inter-firm collaboration.