Internet gaming is one of the most popular online leisure activities. These activities, particularly massively multiplayer online role-playing games, deliver pleasure, a sense of achievement, social interaction, and an immersive experience to online gamers. However, excessive online gaming may have negative consequences by limiting real-life experiences. Because of its prominent negative consequences and similarity to other addictive disorders, the loss of control over online gaming was termed 'internet gaming disorder' (IGD) and included in section III of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). In this review, we focus on the literature supporting IGD as an addictive disorder. We review epidemiologic, neurocognitive, and brain imaging studies to provide suggestions for future studies. We also discuss the intensity and frequency criteria used to distinguish subjects with IGD from casual online gamers. Finally, we recommend future studies to confirm the reliability and validity of the DSM-5 IGD criteria.