The most common titanium alloy, Ti-6Al-4V, is at the same time one of the most important materials in aerospace. The reasons are manifold e.g. low density, high strength and excellent fatigue behaviour. The fatigue behaviour is affected by a lot of parameters like microstructure, surface treatment, residual stress state, roughness, type of loading and geometry. A surface treatment like shot peening acts in the surface layer of a component by inducing compressive residual stresses and strain hardening. This is an important influencing factor for the S/N-curve of the material. With a finite element simulation model for shot peening of an unit cell the state of the surface layer can be estimated. Another factor is the microstructure of Ti-6Al-4V. Depending on the microstructure the S/N-curve varies in a wide range. Independent from the microstructure a well done shot peening treatment leads to a better fatigue behaviour. With notched specimens the notch effect has been evaluated, as well as the effect of shot peening according to the stress gradient. Furthermore the fatigue behaviour of Ti-6Al-4V and the effects of shot peening under multiaxial loading has been estimated.