Rarefied gas dynamics arose originally as the study of gas flows where the average distance between two subsequent collisions of a molecule (the so-called mean free path) is not negligible in comparison with the flow characteristic spatial dimension. In this case the gas cannot be considered as a continuum medium and the Boltzmann transport equation must be used to understand the physics of the system. In addition, due to the increased surface-to-volume ratio, the details of the gas interaction with the limiting (solid or liquid) boundaries gain increasing importance as compared to standard fluid dynamics.
Prompted by the problems raised by the space exploration of the early 60s, when the study of the Boltzmann equation was in its infancy, the International Symposium on Rarefied Gas Dynamics was established and its first symposium was held in Nice, France, in 1958.
Since then, the conference has been the place to discuss problems related to the study of the mathematical properties of the Boltzmann equation, the development of model kinetic equations that could be more easily solved while providing accurate approximations to the physics of interest, algorithms for the numerical solution of the Boltzmann equation (DSMC, spectral solvers, moment methods) and all related applications.