Quantum information theory (QIT) studies how information is processed in the most fundamental level and characterizes capabilities of quantum systems in information processing, for instance, in communication, cryptographic protocols, and computation. It unifies our understanding on physical systems in the aspect of information processing. I approach quantum theory with an information-theoretic view, present its information applications, and discuss the on-going and future directions. QIT is to future information technologies with quantum theory, as information theory is to present information technologies with electromagnetic systems.