When a thin, flat plate executing linear oscillations in its own plane is immersed in a liquid, shear waves are set up in the liquid, and the liquid exerts a retarding force on the plate. This force, which can be measured by means of an electromechanical transducer to which the vibrating plate is coupled, is a function of the product ηρ of the coefficient of viscosity and the density of the liquid. Electrical measurements thus permit a computation of the value of ηρ. A viscometer which operates on this principle and is simple in both construction and use is described. This instrument gives instantaneous indications of ηρ over a wide range and also permits continuous indications of ηρ as a function of time to be made. A theory based on the impedance offered to an infinite vibrating plate by a liquid in which it is immersed is shown experimentally to give a valid, approximate description of the performance of the vibrating‐plate viscometer in its practical form.