ESDU 90031 describes the circumstances under which fretting fatigue occurs in metals and provides guidance on avoiding it. Depending on the loading conditions, fretting can reduce the fatigue strength (to failure) at high endurances by 90 per cent of the unfretted fatigue strength. For diagnostic purposes, notes are included on the physical appearance of a fretting fatigue failure. This document is primarily intended to assist in the interpretation and use of a large number of other ESDU documents in the Series that provide data on the fatigue strength of components under the influence of fretting.