Fatigue is the weakening of a materials subjected to repeated loading and unloading i.e. cyclic loading. If the loads are above a certain threshold, cracks will begin to form at stress concentrators such as the surface irregularities, persistent slip bands or internal defects. After a number of fatigue cycles a crack will reach a critical size and the structure will fracture. Our research has focused both at experimental work of fatigue and thermomechanical fatigue in Titanium and Inconel alloys as well as at modelling of the growth of microstructurally short cracks, in the order of the grain size of the material, using discrete dislocation techniques.