In the early decades of the twentieth century, the emergence of a novel corporate form – the non-profit family philanthropic foundation – created a new instrument through which the charitable impulses of their founders could be expressed. This archival dissertation project examines the histories of these foundations through a few targeted test cases (the Henry R. Luce Foundation, the Pew Charitable Trusts, and the Lilly Endowment, Inc.) and the group of theologically and politically conservative businessmen who engineered them. On a fine-grained level, I aim to document the shift from the religiously influenced, often denominational, charitable institution to the highly “rationalized” modern non-profit philanthropic foundation between the years 1934 and 1959. In so doing, I aim to shed further light on the religious rationalities of some of our nation’s most powerful secular institutions.