The fatigue/fracture behavior of adhesively-bonded pultruded glass fiber-reinforced polymer (GFRP) joints is significantly affected by the loading ratio. This effect is analyzed in this chapter through a complete fatigue/fracture database, derived during recent years, and correlated with the exhibited failure processes of the examined joints. A phenomenologically based criterion is then used for the simulation of the exhibited behavior and the prediction of the fatigue/fracture behavior of the examined joints under different loading conditions. It is shown in this chapter that, upon accurate estimation of the model parameters, it is possible to reliably predict fatigue crack growth curves for several unknown loading conditions, thereby assisting the development of methodologies for the fatigue life prediction of joints under realistic loading conditions.