The second chapter gives a derivation of out-of-equilibrium fluid dynamics from first principles, based on the framework of effective field theory. Main results such as the Euler equations, Navier-Stokes equations, BRSSS equations are recovered and the divergence of the hydrodynamic gradient expansion is discussed. Novel features such as the Borel summability of the divergent series, hydrodynamic attractors, the role of nonhydrodynamic modes and far-from-equilibrium hydrodynamics are described. The chapter closes by a modern derivation of fluid dynamics in the presence of thermal fluctuations.