Manufacture by welding almost invariably introduces defects such as cracks and porosity. For safety-critical items such as aircraft and pipelines, the failure of a component due to the presence of a flaw can threaten human life, as well as having severe economic and environmental consequences. Some flaws, however, are harmless, as they will not lead to failure during the lifetime of the component. A fitness-for-service (FFS) procedure allows flaws to be evaluated consistently and objectively, using fracture mechanics principles. This talk will review the major FFS procedures and give examples of how they can be applied in practice.