Separation of Duty (SoD) is a fundamental security principle that ensures critical tasks or functions are divided among multiple users to prevent fraud. The topic of SoD spans over many different areas, such as Identity and Access Management, Workflows, Petri nets, or high-level enterprise management. In this survey article, we conduct a systematic and stand-alone literature review on SoD. We develop a multi-level classification scheme and analyze the state-of-the-art and current trends in SoD research as well as the current challenges and potential research gaps. To the best of our knowledge, this is the first effort to comprehensively survey and structure SoD literature.