This essay deals with air, the conditions given by and made by architecture. Air, this "invisible by nature," is no less an agent of respiration, a vehicle of the senses, and a relational environment than it is physically measurable. At the crossroads of the design, perception, and action of the environments we inhabit, this element is here placed within the theory of atmospheres. During the modern era, this was the critical association of the airtight glass pane and precise breathing, as seen in Le Corbusier's Salvation Army building. Today, it is the gamble of aerodynamic variability and the porosity of building envelopes, as at the Parisian Mie de Pain. Two large-scale shelters, seemingly diametrically opposed, are the subject of in-depth investigation. The Nantes School of Architecture is considered, through the contrasts of its climatic regimes, as both an activator and a metaphor for a praxis combining study, fabrication, and full-scale experiments. The vast, fluid exchange formed by the Rolex Learning Center in Lausanne is understood as both the agent and the allegory of a relational dynamic that multiplies the fleeting interactions, postures, and appropriations of its occupants. For this work, within the current ecological, economic, and technological context, questions the capacity of architecture to share its atmosphere with communities of users. Ventilatory generosity versus energy efficiency, program uncertainty and freedom of practice, system efficiency and refined regulations: a new democracy is at work, at the crossroads of atmosphere and community, where the delivery of these air conditions is presented as a crucial issue.