Networks of Innovation offers a historical perspective on the manner in which private sector organizations have acquired, sustained, and periodically lost the ability to develop, manufacture, and market new serum antitoxins and vaccines. The primary focus is on the H. K. Mulford Company, on Sharp & Dohme, which acquired Mulford in 1929, and on Merck & Co., Inc., which merged with Sharp & Dohme in 1953. By surveying a century of innovation in biologicals, the authors show how the activities of these three commercial enterprises were related to a series of complex, evolving networks of scientific, governmental, and medical institutions in the United States and abroad.