This chapter illustrates some aspects regarding the quantification of the fretting wear degradation using the friction energy approach. Because friction energy takes into account the friction coefficient, it appears more reliable than the usual Archard work theory in predicting the fretting wear volume extension. However, many investigations underline that the energy wear coefficient (α) is not constant but depends on the wear mechanics involved in the fretted interface which itself depends on the loading conditions. To interpret such fluctuations a multiphysics approach combining Third Body Theory (TBT) and Contact Oxygenation Concept (COC) is developed. By providing a local description of surface wear damages this approach allows to predict pure abrasive “U-shape” but also abrasive-adhesive “W-shape” fretting scar morphologies. Finally, by better predicting the wear depth extension it is also possible to better quantify the durability of fretting wear palliatives like solid lubricants but also hard coatings.