Theory of interpreting is a dynamically developing field of study dealing with various aspects of oral and sign language translation in its several modes and a wide range of settings. The current output of publications (articles and books) in the field can be estimated at a few hundred a year. As opposed to the beginnings, when most studies were published in French or in English, today there is a much more heterogeneous scene, with a lot of recent studies being published exclusively in Japanese, Korean, or Chinese. Topics related to interpreting are popular choices for diploma, MA, and PhD theses. Interpreting research poses a number of challenges, many of which are unique to the field. The aim of this entry is to briefly present the major investigative approaches which have become established over time, giving some examples of prominent studies representing them.