Among the most appalling cruelties perpetrated throughout the course of the Second World War was undoubtedly that of human medical and military experimentation conducted upon both living and deceased human beings. The various Nazi human experimentation programmes were initially carried out not so much in the pursuit of any particular scientific discipline, but largely as a result of the Third Reich’s obsession with race and eugenics. However, this criminal sub-discipline of the Nazi fascination, with its warped racial ideologies, was excused as little other than collateral damage by many of the Nazi physicians and their assistants. Germany’s Axis ally, the Japanese Empire, notorious for its cruelty and sadism ran its own independent programmes of human experimentation such as Unit 731 where human beings were not only subject to the most appalling abuses but were injected with cocktails of poisons and/or diseases and in some instances were dissected while fully conscious without any anaesthesia being administered beforehand. It can be said that both Third Reich Germany and Imperial Japan had a more or less inexhaustible supply of human Guinea pigs throughout the Second World War for its ghastly enterprise in human medical experimentation. These unfortunate souls consisted largely of concentration camp inmates or in the case of the Japanese the indigenous peoples of the lands they conquered along with British, American, Indian and Australian Allied prisoners of war. Yet what was the true purpose of these so-called experiments and what requisites if any were, they to serve? And does any evidence suggest that mutual cooperation existed between Nazi Germany and the Japanese Empire towards the collation of data through the execution of these ghastly endeavours? Another facet examined within this work is why those Japanese physicians involved in human experimentation and medical torture were excused indictments for war crimes when the evidence against them was clearly so overwhelming? And is there any truth to suggest that the Allied powers benefited from the material obtained through questioning at the end of the Second World War? The complicity of both the German and Japanese pharmaceutical companies also has to be brought into question as many cooperated willingly with the military making handsome profits in the process. This work is written in an attempt at analysing all of these factors within the context of a single volume, utilising the testimonies of perpetrator and victim through many new first-hand and archival sources. This volume also serves as a horrifying and sobering reminder of the capability of man’s inhumanity through two of the worst military regimes of twentieth-century history.