This chapter presents a broad overview of Section XII Transport Tank Code, which provides rules for construction and continued service of pressure vessels used in the transportation of dangerous goods via highway, rail, or water. It begins with an overview of the scope and general requirements of the Code including rules on pressure relief devices, stamping, marking certification, reports, and records. The scope of the Code applies to pressure vessels 450 L and above, including additional components and criteria addressed in Modal Appendices that are to be used along with applicable regulations and laws. The Modal Appendix covers Categories 406, 407, 412, 331, and 338 cargo tanks permanently mounted on trucks or wheels used for transporting hazardous materials over public roads. The sections on materials and design rules cover design conditions and allowable stresses, design temperatures, design and allowable working pressures, the design of formed heads, and external pressure design. The coverage also includes information on flat heads and covers, openings and reinforcements, the design of welded joints, and articles covering portable cryogenic tanks including materials and design. The rules for fatigue design are also given in the article covering portable cryogenic tanks. The sections on fabrication, inspection, and testing provide information on general requirements for tanks fabricated by welding; the responsibilities and duties for inspection of transport tanks while being manufactured and for continued service; requirements for nondestructive examination; and rules for transport tanks after they leave the manufacturing facility and are in use by the carriers of hazardous materials.