This paper aims to provide a systematic review on the topic of unlearning (and the related concept of forgetting) to establish the current body of knowledge. Despite the growing popularity of the topic, little research so far has aimed to contribute to the extant literature by providing a detailed examination that includes all aspects of unlearning. Thus, to reach our aim 72 refereed articles were analysed. The findings are synthesised not only in regard to the broad concepts of unlearning and forgetting but also regarding general issues such as operationalisation, research methodology and level of analysis. Based on this a number of research questions are proposed that aim at guiding and informing future research activities. The findings contribute to a more holistic understanding of the topic and complement extant literature on unlearning.