Wheel-to-rail adhesion is fundamental to the operation of a railroad. The potentially high tractive effort of modern diesel-electric and electric locomotives has focused attention more sharply on conditions which limit adhesion. Train stalls, rail burns, flat wheels, and damaged electric traction equipment all point to the importance of the problem. Extensive tests have yielded much information on the causes of low adhesion and methods of improving it. The results indicate that running adhesions in excess of 26 per cent can be maintained by the application of certain materials to locomotive drivers or to the rail.