The applicability and relevance of the terms ‘mutuality’ and ‘reciprocity’ for psychological contract research have been debated. While the terms are widely referred to in studies on psychological contracts, there seems to be no clear consensus on their definitions. Moreover, most existing research has used reciprocity as a theoretical underpinning to help explain the negative relationship between psychological contract breach and employee outcomes. However, considering the conceptualization of reciprocity, such research seems not to have been able to adequately capture reciprocity. The aim of this chapter is to further our understanding of mutuality and reciprocity and assess how these concepts have been defined and operationalized in existing research. A systematic review of empirical studies in which reciprocity and mutuality were examined was conducted. Based on this review, the authors offer proposals for clear definitions and assessments of mutuality and reciprocity. The chapter concludes with several recommendations for future research.