This is the tenth edition of CSA W59, Welded steel construction. It supersedes the previous editions published in 2013, 2003, 1989, 1984, 1982, 1977, 1970, 1946, and 1940. The following is a brief description of some of the most significant changes to the current edition of CSA W59: a) Clause 3 has been revised to add several steels to the prequalified list. b) Clause 5 has been updated to add clarification on the requirements related to hydrogen designators. c) Clause 7 has been reworked to provide clarity on roles and responsibilities for welding inspection. d) Clause 8 includes corrections related to terminology, equipment, and flaw length sizing. Calibration requirements have been revised to reflect digital instrumentation. Allowances for the use of an alternative ultrasonic technique and radiographic imaging systems have been added. e) In Clause 10, all the figures have been reworked into a new format which arranges prequalified joint by joint type rather than by welding process. f) As this Standard contains no commentary, various non-mandatory annexes have been included to generate a better understanding of certain aspects of welded steel construction. The annexes of the previous edition of this Standard have generally been reviewed for clarity. In addition i) Annex W has been added to provide additional requirements for welding consumables, welded fabrication techniques, weld repairs, demand critical welds and welding inspection for seismic-force resisting system (SFRS) of structures. ii) Annex X has been added to define an alternative ultrasonic examination technique for manual conventional and manual phased array ultrasound. New acceptance criteria were developed for equivalent sensitivity to the fixed attenuation (Clause 8.2) technique.