In parallel with the increasing popularity of online games, researchers have reported an increasing number of problematic users. For this reason there is a growing amount of literature analyzing the effects of online games. The present review described the evolution of online games as well as their types and specific characteristics of these types. This review examines (i) the question of definition, (ii) symptoms of problematic use, (iii) the measurement instruments (iv) prevalence data, (v) issues of etiology, (vi) the results of comorbidity, and (vii) the main trends and results in the area of prevention and treatment.