In the first part I will review our work on formulating hydrodynamics as an effective field theory (EFT), which is based on the Schwinger-Keldysh formalism and is implemented in terms of a suitable set of degrees of freedom and symmetries. I will then show how this leads to a well-defined systematic framework to compute loop corrections around the equations of motion of hydrodynamics. I will also show how the formalism extends to magnetohydrodynamics by adding suitable degrees of freedom associated to a magnetic 1-form U(1) symmetry. Finally, I will outline the holographic construction of the EFT of diffusion, which is a baby version of the EFT of hydrodynamics. A crucial ingredient in the holographic derivation is a new analytic continuation in a double-sided black brane geometry.