In this work, a new method is used for the exact vibration analysis of plates with classical boundary conditions. Four classical edge conditions are included: Cclamped, S -Simply supported, Ffree, and Gguided. For square plates, all the possibilities add up to 55 cases. The solutions for the natural frequencies of the plates are found in this paper using static analysis. Starting from the equations of motion of an isotropic rectangular thin plate supported on Winkler elastic foundation, with a positive or negative value, the solution for the vibration frequencies of the plate is equivalent to¯nding the values of the negative elastic foundation that will yield in¯nite de°ection under a point load on the plate. The solution is composed of three parts, the sum of which satis¯es exactly both the¯eld equation and the boundary conditions. For zero force, the vibration frequencies are found up to the desired accuracy. Benchmark results of the¯rst six normalized natural frequencies, of isotropic square plates, for all possible 55 combinations of classical boundary conditions are given, many for the¯rst time.