Prepublication peer review is a cornerstone of science. Overburdened reviewers invest millions of hours in this voluntary activity. In this scoping review, we aimed at identifying motivations for performing prepublication peer review of scholarly manuscripts. Original research studies investigating actual peer reviewers' motivations were included. We excluded modeling studies, studies related to other types of peer review, guidelines, peer review processes in particular journals. Medline, WoS, and Scopus were searched in February 2016, with no language or time limitations, and the search was updated in July 2019. The search yielded 5,250 records, and 382 were chosen for full text analysis, out of which 10 were appropriate for synthesis. Reference snowballing identified one eligible study. Eleven studies were appropriate for synthesis: four qualitative, four mixed qualitative/quantitative, and three qualitative studies, published from 1998 to 2018, involving 6,667 respondents. Major internal incentive was "communal obligations and reciprocity." Major external incentives were "career advancement," "being recognized as an expert," and "building relationships with journals and editors." Major disincentive was the "lack of time." Editors could incentivize peer review process by choosing highest quality articles, improving communication with peer reviewers, in order to make the process of peer review as short and efficient as possible. The gaps in research concern disincentives to review.