The Hydrogen Safety, Codes and Standards program element of the US Department of Energy?s Fuel Cell Technologies Office provides coordination and technical data for the development of domestic and international codes and standards related to hydrogen technologies. The materials compatibility program task at Sandia National Laboratories (Livermore CA) is focused on developing the technical basis for qualifying materials for hydrogen service, i.e., accommodating hydrogen embrittlement. This presentation summarizes code development activities for qualifying materials for hydrogen service with emphasis on the scientific basis for the testing methodologies, including fracture mechanics based measurements (fracture threshold and fatigue crack growth), total fatigue life measurements and full- scale pressure vessel testing.