Recent research in the social sciences reveals that anti- fat discrimination is on the rise in the U.S. Much of this literature suggests that the escalating levels of anti-fat bias have coincided with the onset of the obesity epidemic in this country, and such bias targets the sub-population experiencing the highest rates of overweight and obesity : low-income women of color. But, scholars have shown that high levels of anti-fat derision targeting this sub- population precede the obesity epidemic. Indeed, fatness was stigmatized and associated with poor, immigrant, and black women even before it was thought to be unhealthy, yet very little is known about why this might have been the case. This dissertation explores how fatness became stigmatized and associated with low- income black and immigrant women. Historians have shown that the American mainstream aversion to fatness, as well as the attraction slenderness, developed by the early 20th century. Moreover, previous scholars have shown that scientific understandings of the body during this era came not only from the field of medicine, but also from the natural sciences and anthropology. Thus, I analyze relevant literature from the medical, anthropological, and natural sciences, as well popular literature describing fat and thin bodies from the late 18th - early 20th centuries. The results indicate that fatness became both stigmatized and racialized as early as the late 18th century, as it was seen as evidence of "barbarous" indulgence and associated with blackness. Thinness was simultaneously viewed as evidence of "civilized" self- discipline and associated with whiteness. Fat and thin bodies were gendered and classed during the 19th-early 20th centuries, as slimness was used by upper and middle-class white women as a sign of their "cultivation," and thus marriageability, vis à vis the "coarse," fat "racial others". It was not until these associations were already in place that the medical establishment discovered excess fat tissue was unhealthy. This project is significant in that it exposes the legacy of anti-fat discrimination impacting poor women of color in the U.S. as more than a simple response to the adverse public health consequences of overweight and obesity; rather, fat stigma has been historically raced, gendered, and classed and used to validate social inequality