In addition to microstructure, defects and roughness of additively manufactured metals and structures determine the fatigue behavior and damage tolerance in technical applications such as aircraft turbines and medical implants. Suitable testing strategies and measurement techniques enable the precise monitoring of the process-related influences on fatigue performance. Intermittent fatigue testing enables to investigate the interaction between microstructure, porosity, and crack initiation until the very high cycle fatigue (VHCF) range. The steel 316L, and alloys AlSi10Mg, Ti6Al4V, TNM (TiAl) and IN718 were evaluated in terms of the effect of defects, building directions and stress ratios on fatigue strength, which were correlated with hardness and effective defect or pore size relative to the loading direction using Murakami and Shiozawa approaches. The investigations demonstrate the potential to improve fatigue performance and damage tolerance based on fundamental process-structure-property-damage relationships which are integrated into unified approaches. In order to transfer the mechanisms of solid materials to more complex structures, lattice structures were investigated. Current studies inside the DFG research unit 5250 focusing on the mechanism-based characterization of TPMS structures for patient-specific medical implants with tailored functionality based on innovative methods. In order to minimize the effect of stress shielding, the stiffness of these implants can be adapted to the bone by using adapted lattice structures. Using intermittent µCT scans and specific measurement techniques such as digital image correlation, fatigue failure was localized and an understanding of the complex damage evolution of lattice structures was established.