Besides the ability of making learning more interesting, educators and researchers have been exploring other pedagogical potentials of computer games. How to employ games for constructivist learning and teaching has become an attention in the field of education and game design in recent years. This article gives an introduction to game-based learning. On top of discussing games' intrinsic educational traits from the motivational, cognitive and socio-cultural perspectives, we also review two recent foci of game-based learning. The first one is "education in games" which is an approach for adopting existing commercial games for educational use. The second is "games in education" in which the games are designed specifically with underlying pedagogy for some curricula.