This document proposes a classification of the concepts of ventilated double facades, also referred to hereafter in this document as "VDF". The main classification adopted here (see Part 2) offers a coherent solution for unambiguously describing the various VDF concepts encountered in practice. In order to integrate oneself into the international context, various classifications used in the literature were considered before developing this proposal. A great deal of work was done in order to clarify the terminology associated with these facades. Numerous versions were discussed before arriving at this proposal, which forms the object of the broadest possible consensus among the many persons to whom it was submitted. This document neither describes the performances of the facade concepts presented nor considers their technological aspects. These aspects are dealt with by other specific documents developed within the framework of the project mentioned below. This document was developed within the framework of the second biennial of the Ventilated Double Facades project financed by the Ministry of Economic Affairs in Belgium. Part 4 includes a portion of the document Source book for a better understanding of conceptual and operational aspects of active facades written within the framework of the first biennial of this project. That source book has now been replaced by the present document. Indeed, as a result of the additional knowledge accumulated during the second biennial of this project, some parts of the above-mentioned document have become obsolete and thus have not been included here. Only the relevant parts were integrated into the present document.