This chapter explores the glaring scientific differences in the human health assessment of the popular herbicide glyphosate between European and American institutions. The International Agency for Research on Cancer (IARC) classified glyphosate as a probable human carcinogen, while the U.S. Environmental Protection Agency (EPA) concluded that glyphosate is not likely to be carcinogenic to humans. Both IARC's and the EPA's carcinogenic risk assessment processes are discussed. This work reveals uncertainties in the sciences of toxicology and epidemiology, as well as assumptions made in their applications for evaluating glyphosate. These uncertainties, along with the political context of chemical risk assessment, are at the root of the divergent findings on the carcinogenic risks of glyphosate.