This paper is one of a series of papers presenting research results from the Monitas Joint Industry Project (JIP). The paper focuses on the application of the Fatigue Damage Sensor (FDS) for monitoring of fatigue life consumption of FPSOs. The sensor has been developed by Kawasaki. It is a passive sensor similar in size and installation to a conventional strain gauge. The paper describes the sensor and compares its readings with conventional fatigue assessment methods based on the rain-flow counting of measured strains.