The aim of the research is a detailed investigation of the definition of the nature of Transmissible Spongiform Encephalopathies (TSEs) including scrapie, BSE, and CJD in the United States and Britain between the 1960s and the present. Bovine Spongiform Encephalopathy (BSE) and new variant CJD (nv CJD) have become the subject of increasing debate and controversy involving many different professional and non-professional groups. Some groups of scientists have examined the nature of the fatal disease since 1960s by studying a prototype of mad cow disease, scrapie in sheep. The project focused on the detailed experimental procedures and controversies between scrapie researchers. While there are many different hypotheses regarding the cause of scrapie, BSE and nv CJD, currently the majority of scientists accept a hypothesis called “prion theory”. Prion theorists claim that the disease is caused by abnormal proteins that contain no DNA, which has long been regarded as the blueprint for every single life form. This theory has held centre stage of the severe controversy, but the scientific community has gradually come to accept the prion theory. However, some scientists still do not agree with this view. To understand these contemporary circumstances necessitates an examination of the history scientific disputes relating to scrapie, and my research analyses how competing hypotheses have achieved and lost their credibility within the scientific community and wider arenas.