[en] The INTERNATIONAL STANDARD ORGANIZATION (ISO) in 1986 asked a group of experts, representing about 15 countries, to write a standard concerning the leakage testing of packages for the safe transport of radioactive materials. This gave birth to the Working Group ndeg10 (WG 10) of the Sub Committee 5 'Nuclear Fuel Technology' (SC 5) whose activities are overviewed by Technical Committee 85 'Nuclear Energy' (TC 85). The work of the WG 10 focused on the development of procedures to determine appropriate gas leakage rates and procedures for carrying out leak tightness tests. Such procedures are currently used but are often applied differently. The work was carried out with particular concern to provide for the future users of the standard (ie package designers, shippers of radioactive materials and Competent Authorities), a reference document which is accepted and used by the largest possible number of countries and provides the maximum help to all concerned. The standard pertains specifically to type B packages for which the regulatory containment requirements are specified explicitly. It specifies leak tightness definitions and test methods for demonstrating that packages comply with the regulatory requirements at the Design, Fabrication, Preshipment and Periodic stages. (J.P.N.)