Avatars are growing in popularity and are present in many interfaces used for computer-mediated communication including social media, ecommerce webpages, and organizational applications. Despite their prevalence, the Communication literature lacks a systematic evaluation of existing research on avatars. An examination of this literature reveals similarities but also notable discrepancies in conceptual definitions and operationalizations. Further, research situates avatars across several facets of the basic communication model: as senders and receivers, as an aspect of the channel, and as a form of feedback. Our review synthesizes previous research in four areas. First, we examine how scholars have conceptualized the term “avatar” and identify similarities and differences across these definitions. Next, we examine research that has sought to explain avatar selection and design. Here, we review both motivations in CMC contexts (such as self-presentation and identity expression) and potential effects (i.e., the Proteus effect). Following, we review theoretical perspectives on avatar perception (e.g., the computers as social actors framework). Then, we examine avatar characteristics that communicators evaluate. We identify ways in which communicators evaluate the humanity of an avatar (anthropomorphism, form realism, behavioral realism, and perceived agency) and discuss implications for communication outcomes. We also review findings on the social categorization of avatars, such as when people apply categories like sex, gender, race, and ethnicity to their evaluations of virtual representations. Finally, we consider future directions for avatar research. From a research perspective, we also argue for avatars not just as a topic of study, but also as a tool for understanding other elements of human communication. Avatar-mediated environments provide researchers with a number of advantageous technological affordances that can enable manipulations that may be difficult or inadvisable to execute in natural environments. We conclude by discussing the use of avatar research to extend communication theory and our understanding of communication processes.