Comparing the effect on private R&D investments of allowing firms to cooperate in R&D with that of providing R&D subsidies reveals that in general the latter policy is more effective than the former in promoting R&D activity. Analyzing the implementation of both policies simultaneously reveals that subsidizing cooperative and noncooperative R&D leads to the same market outcome. The preferred R&D-stimulating policy is to subsidize optimally an agreement according to which firms only share the outcomes of their independent research.