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The objectives of this project are to give quantitative answers the following general question: “If one breathes a given gas mixing, which may contain physio-chemical agents such as molecules, particles or sprays, at which rate and proportions will the pulmonary system will carry them until its deepest parts, and transfer them further into the blood? What will be their impact on the organism?”. This type of question can only be treated by an interdisciplinary collaboration. Indeed, this project gathers a team of physicists, experts in hydrodynamics, mathematicians and physicians, all specialists of transport and transfer through the human pulmonary system. Among others, the expected results should permit to understand the behaviour of the flow inside the small respiratory bronchioles, the transition between convection and diffusion along the pulmonary branching system, or the effect of the respiratory cycle on the penetration of the various components of the gas inside the lung. Lastly, one should be able to evaluate quantitatively the amount of these components finally delivered into the blood. The model obtained will allow to better understand the effects of several pathologies such as asthma, pulmonary edema or emphysema. The methodology will follow two main axes: one based on numerical simulations of both convective transport and diffusion, within complex three-dimensional geometries that are periodically changing in time. This type of simulation demands a constant interaction between experts both in applied mathematics, hydrodynamics but also physiologists and physicians. The second axis will be experimental. It will consist in experiments in micro-fluidics on flows in branched structures, and also, if needed, experiments on living animals to test and validate the models obtained from numerical simulations, once firmly established. Applications of this study on health are many: impact analysis of environment pollutants on organisms, optimization of respiratory gas mixing for patients suffering from pulmonary diseases or pathologies, and quantitative predictions of the use of the lung as a path for medicine administration. Finally, one should stress once again the opportunity presented by this gathering inside one strong project of scientific personalities coming from various fields, each with large contributions, and who already have successfully collaborated together (as shown in the publication list).