Chapter 58 authored by Hardayal Mehta and Daniel Pappone, provides details of the development of boiling water reactor (BWR) based nuclear steam supply system (NSSS) and the role of ASME Code in its design, material selection, fabrication and in-service inspections. A general background of the development of the BWR product line is first provided including the current offerings (the Advanced Boiler Water Reactor, ABWR, and the Economic Simplified Boiling Water Reactor, ESBWR). This includes the description of the reactor and reactor system design, safety system design and the containment design. The authors next describe the key features of the ESBWR including the natural circulation design, operating domain and passive safety features. The ESBWR core and containment cooling systems represent a radical departure from those of the earlier BWR product lines in that the cooling systems are passive and do not rely on electrically driven pumps. The ASME Code aspects covered include the ASME Code versions used in the construction, treatment of environmental fatigue issues, material selection, and others. Future directions in terms of fabrications, modularization, and others are lastly discussed.