This open access book presents the proceedings of the 33rd International Symposium on Rarefied Gas Dynamics (RGD33), held in Göttingen, Germany, on July 15-19, 2024. It encompasses applications of space, materials, and propulsion, as well as the basic physics of molecular interactions, gas surface interactions, kinetic theory, astronomical observations, gas transport, multi-phase flows, combustion, non-equilibrium hypersonic gas dynamics, and plasma processing. It covers topics such as Boltzmann and related equations, Monte Carlo methods and numerical solutions, gas-surface interactions, high speed flows, shock waves, nozzle expansions, high altitude aerodynamics, jets and plumes, internal flows and vacuum systems, reactive gas dynamics, rarefied plasmas, MEMs and NEMs, granular flows, and porous media.