In 1940 the Museum of Modern Art, New York, (MoMA) became the first major American art museum to establish a curatorial department dedicated exclusively to photography. From the perspective of the photographers, curators, and critics who had sought institutional legitimacy for the medium, the founding of the Department of Photographs was a watershed event, marking the moment when photography finally came to be recognized as a museum subject equal to painting and sculpture. Although the department has since had a pervasive influence on the field and the history of photography, surprisingly little scholarship has addressed its contentious formation. This dissertation seeks to fill this significant gap in the literature by examining the department's inception and the six years Beaumont Newhall served as its curator. Of particular concern are the ideological battles waged over how photography would be presented at MoMA by Newhall, his wife Nancy--who served as acting curator when her husband enlisted in the army during World War II--and the department's co-founder and key advisor, Ansel Adams. As acolytes of the photographer and gallerist Alfred Stieglitz, who himself had long fought for the recognition of photography as a medium of art, the Newhalls and Adams took aesthetic quality as their guiding metric, asserting that in order to raise the profile of photographers, educate the public, and improve standards of taste, the museum should show only the very best work ever created--the "heavy cream" of photographic production. Their vision for photography at the museum was counterbalanced by that of the photographer Edward Steichen and many prominent writers and critics, who argued that MoMA should treat photography as a broad-ranging cultural phenomenon and means of communication, rather than merely as a medium of self expression. The debate between these two camps illustrates the considerable philosophical, interpretive, and museological challenges raised by photography's introduction into the museum, issues that remain as contentious as ever.