Considered to be the latest generation of distance education, e-learning, especially online education, fully employs the power of the Internet and brings education to a new era. As the usage of distance/online interaction is believed to be one of the most essential factors for a successful distance/online course, a thorough understanding of its character becomes necessary for course design. Therefore, the purpose of this article is to help people have a clear picture of distance/online interaction through reviewing various distance/online interaction classifications which include Moore's, Hillman, Willis, and Gunawardena's, Gilbert and Moore's, and Northrup's works. It is expected that the knowledge guides the selection of interaction strategies and enhance learners' learning efficacy in a distance/online learning environment.