This paper presents an ongoing research on computer supported collaborative design carried out by the ARIAM-LAREA laboratory at the Superior National School of Architecture of Paris-LaVillette. The aim of this research is to analyze computer mediated architectural design practices in order to identify the specific “operations of conceptioni. Two observations of architectural collaborative design supported by computer tool called “Studio Digital Collaboratif” have been conducted: one concerning collaboration between architects, in laboratory, the other one between architects and engineers in a real situation of design. Our analysis use two concepts to explain the collaborative conception in architecture: classes of operation of conception and operation of conception. They permit to identify the elementary operations of conception and pragmatic operations of collaboration. According to the first results it seems that classes of operation of conception are shared but operations of conception seem to be unshared.