The aim of this research is to develop a conceptual framework for alternate reality games based on game design theory. Alternate reality games or ARGs are a unique form of game that enables people to collaboratively play a game that is not a game in the context of the real world. To understand ARGs one needs to understand what differentiates them from other types of games as well as what makes them games. The research investigates existing literature of alternate reality games as well literature in the field of game studies to develop a set of characteristics for alternate reality games based on game design theory. Case studies are done on three different ARGs and summaries for the games are created. The phenomena in the summaries are placed into categories and subcategories. The categories and subcategories are developed by analysing the game summaries using constant comparative analysis. Using the categories, subcategories and the relationship between them, diagrams are created for each of the studied ARGs. A detailed analysis of each game is done and a summary diagram is created for each game. The summary diagrams are then combined to create a generalizable diagram for ARGs. The combination of the theoretical framework developed during the literature study together with the generalizable diagram from the analysis of the three games are then combined to create a conceptual framework. The conceptual framework creates a deeper understanding of ARGs and the various phenomena found within them by building on game design theory found in the field of game studies. The conceptual framework can aid in the creation of ARGs as well as enable the further analysis of these games.