A game mod describes a modification within an existing commercial computer-based game that has been created by a user. By game modding, a user can participate in the creative process by taking the setting of his or her favorite game and customizing it for entertainment purposes or to convey information. For years, commercial computer-based game developers committed considerable resources toward preventing users from hacking into or hijacking their games. Now several computer-based game developers provide editors with their products to encourage users to create content and to allow educators, for instance, to take advantage of the benefits and production quality of commercial computer games in order to create customized instruction. This article focuses on mainstream, accessible games with straightforward modding tools that easily can be integrated into a learning environment.