Driveline constant velocity joints are an unusual contact application with grease lubricated elements oscillating over variable small distances with rolling and sliding motions. Contact stresses are high and surfaces are predominantly boundary lubricated. Contacting materials must have structural integrity and a high resistance to surface and sub-surface fatigue and wear.In the development of constant velocity joints, extensive testing is carried out on rigs and vehicles, in addition to normal service proving trials. These include specific fatigue tests for the refinement of life prediction models. Aspects of material damage characterisation from these tests, and from service, are discussed.