Research shows that feedback can have large positive effects on student achievement, but that effects vary considerably. Some of the variables that influence feedback’s effects are the characteristics of the feedback. When making decisions on which research to pursue, knowledge about the focus of previous research is useful. We conducted a systematic literature review of studies that address feedback in mathematics. The aim was to identify which feedback characteristics are addressed in the reviewed publications, which characteristics have been given ample research attention and which have been neglected. We searched for publications from 2012–2021 in three bibliographic databases: ERIC, Psychinfo, and Academic Search Premier. We identified 12 feedback categories and 5 variables which together describe the characteristics of the feedback in the publications found in the literature search. Feedback about the correctness of students’ answers and solution processes were common characteristics, while feedback on students’ self-regulation was uncommon.