Taking the criteria of sustainability into account in the design process involves interactive optimization between the environmental, socio-cultural and economic criteria of the project. As the principle climatic interface and an important architectural component, the façade represents a fundamental element in this context, as shown by the one specifically developed for the Federal Office of Statistics (FOS) tower in Neuchâtel. Intensive collaboration between architects, engineers and constructors indeed results in high performances in terms of energy consumption and comfort, while simultaneously contributing considerably to the building’s expression and identity.