Fatigue crack monitoring is essential to Ship and Offshore structures, in order to guarantee structural integrity and safety on board. Regular inspections, which are currently performed manually are hazardous, costly and infrequent. The CrackGuard JIP has the goal of developing a system for reliable monitoring of fatigue cracks based on the characteristic magnetic pattern that occurs around a fatigue crack as a result of magnetization by the Earth magnetic field. This method, which is called the Self Magnetic Flux Leakage method, makes use of the disturbance caused by a fatigue crack on the magnetic flux inside the material and can be detected by a leakage pattern of this magnetic flux around the fatigue crack. The application of the self magnetic flux leakage method for fatigue crack monitoring on a full-scale structures demonstrates that the method is very suitable for monitoring fatigue cracks in ship and offshore structures. The amplitude of the observed flux leakage pattern is increased by the large amount of ferromagnetic materials in these structures, which improves crack monitoring and even allows for the tracking of a propagating fatigue crack on the bases of the obtained measurement results.