Statistical mechanics (SM) is a branch of theoretical physics that explores cooperative phenomena observed in many body systems. For a long time, applications of SM were limited to material objects such as gases, liquids, metals, magnets, and semi-conductors. However, about a decade ago, concepts and methods developed for SM began to be actively applied to problems in information science. These applications have provided various ground-breaking results, particularly in the fields of communication and computation. Such activities are still ongoing, resulting in the development of a novel cross-disciplinary research field between the natural and the information sciences. In this review article, we show why and how SM can be utilized in information science, illustrating its use by means of three applications: error correcting codes, a public key cryptosystem, and analysis of a decision problem.