AbstractDuring the period of extension of the ITER EDA the ITER Test Blanket Working Group (ITER TBWG) continued its activities to co-ordinate the R&D work performed by the Parties and to develop a test program on ITER for a DEMO-relevant tritium breeding blanket. The ITER parameters have been revised during this period and it was not clear that for new conditions a reasonable test program could be developed. Considerable extrapolations have to be made from the ITER conditions to those of a potential fusion reactor. To cope with the problems an approach to testing based on the ‘act alike’ principle has been developed. Key aims of the tests are code validation and verification of design assumptions based on calculations and results of out-of-pile or in-pile experiments. It is shown that most of the important breeding blanket functions can be investigated with the parameters of ITER, and that the blanket test program can be synchronized with the machine operational scenario. It is recommended that a strong effort be maintained on this area of R&D in the future.