Recently we have presented an extended theory for molecular mass transport (Kerkhof and Geboers, 2005). We have indicated the possibility, and the need, to define a new framework for studying and teaching the theory of multicomponent molecular transport in fluids (Kerkhof and Geboers, 2004). Here a new, structured, overview of the subject is presented. An analysis is given of complicated issues in textbooks and review papers. (c) 2005 Elsevier Ltd. All rights reserved.