This document specifies a general outline of the ISO 3834 series and criteria to be taken into account for the selection of the appropriate level of quality requirements for fusion welding of metallic materials, among the three levels specified in ISO 3834-2, ISO 3834-3 and ISO 3834-4. It is applicable to manufacturing, both in workshops and at field installation sites. This document does not specify requirements for a total quality management system (QMS). However, Clause 6 identifies QMS elements where their inclusion complements the ISO 3834 series.