A splined coupling comprises a radially inner shaft and a radially outer shaft having a cavity for receiving the inner shaft. First splines are provided on a radially outwardly facing surface of the inner shaft. Second splines are provided on a radially inwardly facing surface of the cavity of the outer shaft. The first splines are slidably engaged with the second splines. At least one biasing element, for example a diaphragm is arranged to act between the radially inner and radially outer shafts for locating the first splines in a desired axial position relative to the second splines and to provide a biasing force resisting the axial movement of the first splines relative to the second splines upon relative axial movement of the inner and outer shafts.