An investigation of retreating blade stall on a model helicopter rotor has shown that a series of separate pressure distribution and boundary layer events lead up to complete blade stall. Dynamic overshoot of the static stall values appears to be followed by the shedding of a vortex from the leading edge, analogous to the stalling process on an oscillating wing. This experimental picture of the local flow field was derived from measurements of blade element pressure and skin friction distributions, surface streamline directions, and local angle of attack. The results of the experiment also demonstrate the limitations of contemporary empirical corrections in accounting for three‐dimensional and unsteady effects on classical airfoi1 data after complete stall occurs. From the resutls of this test, it is postulated that the basic retreating blade stall mechanisms become increasingly dominated by dynamic vortex shedding as advance ratio increases.