There are currently many approved biologic products throughout the world, providing huge benefits across many therapeutic areas. At the present time, a number of biologics are coming off patent, which has opened the door to biosimilars. A biosimilar is a proposed biologic product which is highly similar to an already licensed/marketed biologic product, but because of the complexities of manufacturing biologics, it is not an exact copy. Proposed biosimilars can generally follow a tailored regulatory pathway with reduced development costs and time, with a goal of demonstrating no clinically meaningful differences based upon the totality of evidence. Global regulations vary in their requirements, and currently there is a lack of harmonization regarding exactly how much abbreviation of the nonclinical portion of biosimilar development is acceptable and appropriate. This presentation will review regulatory guidelines, discuss reasons why nonclinical in vivo studies are currently being conducted, discuss whether there has been value from those studies, and present a case for why nonclinical in vivo toxicity studies may not be necessary in support of many biosimilar development programs.