ISO 6520-1:2007 serves as the basis for a precise classification and description of weld imperfections. In order to avoid any confusion, the types of imperfection are defined with explanations and illustrations where necessary. Metallurgical imperfections are not included. Another system for the designation of imperfections is possible according to ISO/TS 17845. A correspondence is given between the existing classification of imperfections according to ISO 6520-1:2007 and the designation system according to ISO/TS 17845:2004.