A rail fastening device comprises a clip (10) having a base (11) and a nose (12) for engaging a rail flange (F). The base (11) comprises circular aperture (14) in which a circular cam (13) is rotatably mounted, the cam (13) being provided with an eccentric aperture (24) for receiving a ground anchor (25), the cam aperture (24) being radially offset from the rotational centre of the cam (13) to define a cam lobe (15). The cam (13) may comprise a ramped circumferential shoulder (18) to engage a complementary shoulder (21) inside the base aperture (14) such that any rotation of the cam (13) under the applied load of the rail causes the cam (13) to move axially of the base aperture (14) thereby tightening the engagement of the anchor (25) on the cam (13) and preventing movement of the clip (10). The degree of rotation of the cam (13) may be limited so that it can only turn in the tightening direction under load.