Peer assessment is a popular research topic as it takes place in multiple educational settings around the globe. Due to its nature, a number of intrapersonal and interpersonal factors are involved. Empirical research on these factors has been increasing and our aim was to systematically review them to extract conclusions about the relationships between peer assessment and intrapersonal and interpersonal factors. Using different search strategies, we reviewed 69 articles. We investigated: (1) the characteristics of the included studies, (2) the trends in the bidirectional relationships of intrapersonal [left right arrow] peer assessment and interpersonal [left right arrow] peer assessment, (3) the empirical findings in the relationships between intrapersonal factors and peer assessment, and (4) the empirical findings in the relationships between interpersonal factors and peer assessment. We identified six intrapersonal factors: motivation, self-efficacy, emotions, trust in the self as assessor, fairness, and comfort; and five interpersonal factors: social connections, trust in the other as assessor, psychological safety, value diversity/congruence, and interdependence. The results showed clear directions for some of those factors and preliminary in some of the others. This review offers directions to improve the quality of peer assessment research and explores the role of bidirectionality for future research, including an instrument to report the characteristics of future peer assessment studies to facilitate better reports and research designs.