This chapter is a review of the basic equations and concepts of fluid dynamics. These also form the foundations of aeroacoustics. We will start by considering the equations of fluid motion, the thermodynamics of small perturbations, and the role of vorticity. We will then evaluate the propagation of energy in the fluid, including the energy associated with sound waves in a moving medium, sound power, and acoustic intensity. Finally, we will review some basic concepts of fluid dynamics and summarize some results and methods of ideal flow theory that are most relevant to low Mach number aeroacoustics.