As a result of a four-year study carried out with the last year students at the Faculty of Translation and Interpretation of the University of Valladolid (Spain), a new approach to the documentation phase is suggested. In this approach, the documentation in interpretation is no longer a systematic collection of equivalencies, but a dynamic process, in which the interpreter must recognise, analyse and study the terminological hierarchies of a given domain. Needless to say that this process carries along the expert knowledge acquisition which the interpreter must include in his/her own knowledge base. This underlying mental structure acts as a platform, which will facilitate the equivalencies between concepts and their various linguistic representations. These networks will vary depending on pragmatic criteria, to which the interpreter must always pay attention.