"Mobile learning", or "m-learning", has become an umbrella term for the integration of mobile computing devices within teaching and learning. In the literature, however, use of the terms has been unsystematic. The purpose of this article is to critically examine the principles of mobile learning. First, I examine the extant literature with regard to defining mobile learning. Four definitions of mobile learning categories are described: (1) relationship to distance education and elearning, (2) exploitation of devices and technologies, (3) mediation with technology, and (4) nomadic nature of learner and learning. Second, in an effort to provide a basis on which to ground future mobile learning research, I propose a framework of design characteristics for mobile learning environments. Seven design characteristics are identified and discussed. Finally, I present implications for future research and instructional design. This paper contributes to the field of mobile learning by providing researchers more precise ways to identify and describe the characteristics of mobile learning environments, as well as describe the attributes of successful mobile learners.