This paper examines what is known so far about the role of open source software development within the world of game mods and modding practices. Game modding has become a leading method for developing games by customizing or creating OSS extensions to game software in general, and to proprietary closed source software games in particular. What, why, and how OSS and CSS come together within an application system is the subject for this study. The research method is observational and qualitative, so as to highlight current practices and issues that can be associated with software engineering and game studies foundations. Numerous examples of different game mods and modding practices are identified throughout.