This thesis aims to provide a general overview of the crime of heresy in England from about the year 1520 until the death of Mary I in 1558. It begins by examining some of the problems inherent in heresy, chiefly its definition and identification, which had special relevance during the fluctuating religious climate of the period in question. It then examines other concepts, namely the need for order, unity and obedience, that profoundly affected the very definition of heresy and the way in which it was viewed as an offence I which in turn led to the adoption of one particular method of addressing and resol ving the si tuation, the policy of persecution. The remaining chapters look at the legal structure that was implemented as a result of these earlier considerations, and finally, examines some of the major heresy cases of the period which illustrate the extent to which the religious offence of heresy could be linked to, and altered by, the political climate and considerations of the day.