The invention relates to a method for mounting a rotor blade with a rotor blade shell and an internal space defined by the rotor blade shell, by at least one rotor blade clamp being applied around the outside of the rotor blade shell, by means of which at least one clamping force is exerted from the outside to the rotor blade shell, directed into the internal space by at least one expansion device being introduced into the internal space, by the expansion device inside the internal space being moved into at least one segment of the rotor blade around which the at least one rotor blade clamp is applied, by the at least one expansion device being expanded inside the at least one segment until at least one outwardly-acting counteracting force is exerted from the inside on the rotor blade shell.