This paper will examine the investment and management activities of a loosely structured group of investors, Andrew Carnegie & Associates, to reevaluate the relative powers of individuals, joint venturers, and corporations in a period of great expansion in the American industrial economy. Carnegie is certainly a well-known figure in American business history, but this decade of associations and activities represented a crucial pivot in his career—and in the larger economy—and it deserves a fresh look for a number of reasons. At the time they were operating, his joint venturers, J. Edgar Thomson, Thomas A. Scott, and other corporate officers, had a variety of reasons to conceal their participation behind Carnegie's name. Unsurprisingly perhaps, Carnegie's modern biographer emphasizes the canny Scotsman's role in spearheading this group's investments in bridge building, telegraphy, railroads, and a range of manufacturing concerns. But Carnegie appears in quite a different light to Alfred Chandler—as the leading missionary for managerial forms and structures. Thus we must choose between a visionary individualist and a corporate architect. Carnegie, however, pointed to the 1865 formation of the Keystone Bridge Company as the fountainhead of his own rise. This paper will draw from a range of original sources on Keystone, its investors, and its clients to offer a new portrait of Carnegie in transition. The paper arises from my larger study of the Eads Bridge, a record-breaking edifice of three steel-arch spans over the Mississippi River at St. Louis, completed (by subcontractor Keystone Bridge Company) in 1874. The paper addresses these questions: How did Carnegie and his colleagues combine an old networking form, the joint venture, and a new networking form, the corporation, to enhance the generation of wealth/profits—for themselves and for the corporations to which they allied themselves? What benefits arose from this mélange of network forms? What problems or conflicts emerged from their interaction?