Video game addiction is the main theme of this thesis. After a brief definition of addiction, the focus is on the specific addictive properties of Internet and games. Massively multiplayer online role-playing games (MMORPGs) are described, as they tend to be the most addictive type of game, with a specific focus on World of Warcraft (WoW). Issues of diagnostic criteria for Internet addiction and Internet gaming disorder (IGD) are be presented.