ETAC is a design office for technical and architectural synthesis located at the gateway to Paris, in Boulogne-Billancourt. We carry out studies in 2D or 3D, working with project managers and architects, accompanying their projects from design to execution, thus facilitating the follow-up of their projects by favouring deadlines and costs. Our solutions are adapted to the needs of each company by offering them different services: - Technical audit and pre-synthesis - Modeling to improve decision making - Technical Synthesis to detect conflicts and provide solutions - Architectural & Façade Synthesis for a better control of the project and the construction process. After several years, associating their knowledge of execution to the service of large Engineering and Architectural firms, ETAC's collaborators have been able to acquire and deepen their experience of technical and architectural studies of the building, the implementation of new procedures of 2D or 3D studies and in particular to apprehend the arrival of the BIM in the world of the construction which we master perfectly. A project is never realized alone. ETAC