In the thesis, I construct a theory of what elements games are made of, and complement the formal, structural approach by applying studies and concepts from psychology in order to understand the experiential and emotional experince of playing games. The theories lead to a number of analysis methods and design implications, which I try to illustrate with a number of case studies. The ‘100+ Games Project’ is a part of the thesis, where I have analysed more than 100 games – across different media ranging from pen & paper to computers – with the methods.