Fluids under control : the 2021 Prague Sum workshop lectures This volume presents state of the art developments in theoretical and applied fluid mechanics. Chapters are based on lectures given at a workshop in the summer school Fluids under Control held in Prague on August 25 2021. Readers will find a thorough analysis of current research topics presented by leading experts in their respective fields. Specific topics covered include: Magnetohydrodynamic systems The steady Navier Stokes Fourier system Boussinesq equations Fluid structure acoustic interactions. Fluids under Control will be a valuable resource for students interested in mathematical fluid mechanics.