Introduction to fatigue strength. Loads occurring during machine operation. Stress characteristics, time-invariable stress, influence of stress concentration, constant temperatures and multiaxial stress state. Mechanical and thermal material fatigue, relevant influences. Time-variable stress with constant amplitude or constant stress ratio. Permanent and time-limited fatigue endurance. Experimental and “synthetic” service life determination, testing programs and equipment. Hypotheses of mechanical and thermal fatigue damages accumulation. Methods for defining stress spectrum. Fatigue strength proof and service life forecasting, influence of multiaxial stress state, concept of nominal stress and hot-spot stress. Review of technical regulations according to field of application. Probabilistic character of proof. Specific qualities of welded part fatigue. Monitoring the fatigue crack growth and prediction of the remaining life-time, based on the fracture mechanics. Shaping the structure components exposed to fatigue.