Criteria are an essential component of any procedure for assessing merit. Yet, little is known about the criteria peers use to assess grant applications. In this systematic review we therefore identify and synthesize studies that examine grant peer review criteria in an empirical and inductive manner. To facilitate the synthesis, we introduce a framework that classifies what is generally referred to as 'criterion' into an evaluated entity (i.e., the object of evaluation) and an evaluation criterion (i.e., the dimension along which an entity is evaluated). In total, the synthesis includes 12 studies on grant peer review criteria. Two-thirds of these studies examine criteria in the medical and health sciences, while studies in other fields are scarce. Few studies compare criteria across different fields, and none focus on criteria for interdisciplinary research. We conducted a qualitative content analysis of the 12 studies and thereby identified 15 evaluation criteria and 30 evaluated entities, as well as the relations between them. Based on a network analysis, we determined the following main relations between the identified evaluation criteria and evaluated entities. The aims and outcomes of a proposed project are assessed in terms of the evaluation criteria originality, academic relevance, and extra-academic relevance. The proposed research process is evaluated both on the content level (quality, appropriateness, rigor, coherence/justification), as well as on the level of description (clarity, completeness). The resources needed to implement the research process are evaluated in terms of the evaluation criterion feasibility. Lastly, the person and personality of the applicant are assessed from a 'psychological' (motivation, traits) and a 'sociological' (diversity) perspective. Furthermore, we find that some of the criteria peers use to evaluate grant applications do not conform to the fairness doctrine and the ideal of impartiality. Grant peer review could therefore be considered unfair and biased. Our findings suggest that future studies on criteria in grant peer review should focus on the applicant, include data from non-Western countries, and examine fields other than the medical and health sciences.