Conceptions of patents have changed significantly over the past two centuries, reflecting broad changes in state structures and the international system. In the late eighteenth century, the creation of democratic states such as the United States and France encouraged the conceptualization of patents as an economic and political right belonging to an individual, rather than to a corporate body such as a guild. A second conception of patents arose in the nineteenth century in which patents become a state-based mechanism for motivating economic growth. In the late twentieth century, patents have become conceptualized as an essential part of the economic infrastructure of a state, for both industrialized and less developed countries. This conceptualization has allowed international development organizations to become central in the diffusion of patent legislation to less developed countries. These changes in conceptions about patents did not always occur smoothly, however. Major controversies over the role and usefulness of patents occurred in each century, implying that the diffusion of patent legislation was by no means inevitable. This paper illustrates these arguments with a historical discussion of patents and a statistical analysis that models the adoption of patent legislation for all countries from 1790–1984.