The project set out to create a theory within game design to help designers create better multiplayer games with basis in the concepts of “Counterplay and Teamplay” described by the game designer Tom Cadwell. The methodology chosen was a Grounded Theory approach, in which the opinion of experts within the field of game design was addressed. This was done through interviews, blog posts, podcasts, articles and books on game design. This data was analysed through various qualitative methods such as line-by-line analysis and extrapolating statements from that. The information lead into generating a number of codes that was further compiled into eight categories, three patterns and finally the theory. The overall outcome of the theory created seems to be an overall success; however, the method used to get there could be documented better. The theory includes the design concepts that are in focus for multiplayer games and tries to give statements that help designers implement these.