Between 1954 and 1998, the tobacco industry funded more than 1,900 research projects at a total cost of $355 million, on topics such as the roles of heredity and nutrition in cancer. Even though legitimate, this research was intended to divert attention from the harmful effects of tobacco. We provide the first formal analysis of such diversion research. We show that special interests may have strong incentives to affect the scientific agenda, even when the research itself is unbiased. This form of scientific lobbying yields large welfare losses and raises concerns about the private funding of research.