Relying on a quantitative analysis of the patenting and assignment behavior of inventors, we highlight the evolution of institutions that encouraged trade in technology and a growing division of labor between those who invented new technologies and those who exploited them commercially over the nineteenth and early-twentieth centuries. At the heart of this change in the organization of inventive activity was a set of familiar developments which had significant consequences for the supply and demand of inventions. On the supply side, the growing complexity and capital intensity of technology raised the amount of human and physical capital required for effective invention, making it increasingly desirable for individuals involved in this activity to specialize. On the demand side, the growing competitiveness of product markets induced firms to purchase or otherwise obtain the rights to technologies developed by others. These increasing incentives to differentiate the task of invention from that of commercializing new technologies depended for their realization upon the development of markets and other types of organizational supports for trade in technology. The evidence suggests that the necessary institutions evolved first in those regions of the country where early patenting activity had already been concentrated. A self-reinforcing process whereby high rates of inventive activity encouraged the evolution of a market for technology, which in turn encouraged greater specialization and productivity at invention as individuals found it increasingly feasible to sell and license their discoveries, appears to have been operating. This market trade in technological information was an important contributor to the achievement of a high level of specialization at invention well before the rise of large-scale research laboratories in the twentieth century.