This chapter describes the impact of formal intellectual property rights on the production and diffusion of "dual knowledge"-ideas that are simultaneously of value as a scientific discovery and as a useful, inventive construct. We argue that a great deal of knowledge generated in academia, particularly in the life sciences, falls into this category (sometimes referred to as Pasteur's Quadrant). The production and diffusion of dual purpose knowledge challenges the premise of most science policy analysis, which is implicitly based on a clear separation between basic scientific knowledge and applied knowledge useful in the development of new technology. Instead, dual knowledge simultaneously makes both a basic and an applied contribution. We review qualitative and quantitative evidence relating to the policy challenges raised by the production and dissemination of dual knowledge, highlighting three broad findings. First, rather than facing a fundamental tradeoff between applied research and more fundamental scientific knowledge, research agencies can and do invest in dual purpose knowledge. Indeed, the dual purpose knowledge framework suggests a distinct rationale for public sector involvement in the funding and conduct of research: the social impact of a given piece of knowledge may be enhanced when knowledge is produced and disclosed in accordance with the norms of the scientific research community (particularly compared to secrecy). Second, we suggest that, within Pasteur's Quadrant, the increased use of formal IPR seems to be significantly shaping the structure, conduct and performance of both university and industry researchers. On the one hand, from the perspective of individual researchers, patenting does not seem to come at the expense of scientific publication, and both respond to the process of scientific discovery. There is some evidence, however, that patent grant may reduce the extent of use of knowledge: the citation rate to a scientific article describing a dual-purpose discovery experiences a modest decline after patent rights are granted over that knowledge. Finally, the impact of patents may be indirect; rather than directly impacting behavior through patent enforcement, scientific conduct may be affected through related mechanisms such as material transfer agreements. Not simply a legal document within a seamless web of cooperation, nor a bludgeon to stop scientific progress in its tracks, patents seem to be changing the "rules of the game" for scientific exchange, cooperation, and credit.