Computer-assisted language learning is a research field which explores the use of computational methods and technologies as well as new media for language learning and teaching. Recently, artificial intelligence techniques have been adopted mainly to improve the interaction between the user and the system. This paper provides an overview about the state of the art in computer-assisted language learning. A set of systems have been investigated and classified along five dimensions: system, language, human skills, language elements, and technology. The paper concludes with a discussion about outstanding problems which still need further research in order to exploit the full potential of new technologies and media in modern language learning environments.