Serious games have drawn attention with positive effects on users in various areas. While many categorizations and definitions of serious games have attempted to elucidate the elusive term, we are still some way off in formulating an agreed understanding of what serious games are and how they can be classified. This paper aims to provide an overall picture of the concepts and categorizations of serious games. From the results of previous literature, the major applications of serious games can be converged into five primary areas: public policy, military, education, corporate and healthcare. Likewise, theories applied to serious games comprise three main strategic purposes: information notification/PR, change of user attitude/behavior, and purposive training. Based on the strategic purposes and applied areas, this study categorizes serious games into 15 sectors. In addition, founded on the motivation factors and the characteristics of digital games, the current study suggests a new definition of serious games.