Student peer review of drafts in progress was a staple of writing instruction for decades before computers: students exchange and discussed typed or handwritten drafts in small groups of three or four. With the advent of digital connectivity, students could circulate electronic versions of their texts, then read and annotate drafts online. Simultaneously, digital peer review systems were developed that not only facilitated student response but included learning analytics as well as features such as repositories of comments to prompt student response, badges, sticky notes, and feedback mechanisms that evaluated the quality of the response; anonymous response also became possible (see Lu & Bol, 2007). After a brief historical introduction, this chapter focuses primarily on digital peer review systems and peer review systems built into LMSs such as Canvas. The chapter describes the nature and range of digital peer review systems and includes a summary of research on their effectiveness.