In recent years there has been increasing need to acquire technology for the safe handling of hydrogen for petroleum and other energy related applications. The pace of research into metal/hydrogen interactions accelerated at the start of the space age due to the hydrogen's efficiency per unit weight as a rocket fuel. Practical applications called for hydrogen to be transported and used at high pressures thereby increasing its hazard potential. Exotic and expensive alloys could be used to put astronauts into space because cost was of little concern where safety was an issue. For most conventional applications steel is still the practical choice. It has been long recognized that at ordinary and elevated temperatures hydrogen can be destructive to steels@ not just to high-strength steels@ but also to steels of ordinary strength levels. Hydrogen's capability to enter and then diffuse through the metallic lattice@ accelerated by stress gradients and seeking out points of weakness where it can concentrate or react@ renders it capable of destroying pressure retaining metals from the inside where damage defies detection and until it is too late and the pressure containment as failed or is no longer safe. Considerable research aimed at understanding hydrogen-steel interactions has been conducted over the last half century. An important objective has been to permit the reliable use of steels of higher strength levels in aggressive hydrogen environments. Tied to this objective is the necessity of fabricating the higher strength steels without cold cracking due to hydrogen introduced during welding. The problems and solutions are complex because of the diverse microstructures and compositions that have been developed to achieve the perfonnance goals set for steels. This Welding Research Council (WRC) Bulletin is part of a series that captures the essential studies of the interaction of steel-hydrogen interactions in recent years. Topics include Modern Vanadium Steels for High Temperature Petroleum Reactors (# 524)@ Fabrication and Repair of Low Alloy Steel Pressure Equipment (# 525)@ Performance ofSteels in Hydrogen Charging Environments (# 526)@ Practical Aspects ofHydrogen Attack (# 527)@ Test Methods for Hydrogen Induced Cracking (# 530)@ Metallurgical Studies ofSteels for Sour Service Environments (# 532)@ Studies ofCladding and Overlayfor Pressure Vessel Service (# 534)@ and Toughness@ Fracture and Fitness for Hydrogen Service (# 535). The papers included have been presented at international conferences sponsored by WRC's sister organization the Materials Properties Council Inc. (MPC). The technology reported in this series provides a comprehensive view of practical solutions to engineering problems and advances in the knowledge about hydrogen and steel interactions