The course is concerned with the fundamental aspects of gaseous fluids. Distinct from conventional and somehow empirical treatments for the macroscopic properties of thermodynamics and fluid mechanics, the underlying structure of gases will be explored. The topics shall cover the equilibrium kinetics, microscopic, quantum-mechanical and statistical-mechanical descriptions of fluid physics. Specifically, three subjects that have not been well accessed to students in mechanical/aerospace engineering, whose significance is gradually appreciated, will be involved, i.e., kinetic theory, quantum mechanics, and statistical thermodynamics. Relying on the progress and available time, some applications such as chemical kinetics and reactions would be discussed in due time.