The nuclear design of fusion devices is based on neutronics calculations. The neutron and photon flux spectra are calculated with 3D neutron-photon transport codes, and the nuclear responses are obtained by convolution with the related nuclear data. These computational tools and data need to be validated through mock-up and benchmark experiments. Typical experiments, carried out in the frame of the European Fusion Technology Programme, are discussed, in particular a bulk shield experiment on a mock-up of the inboard shield of the International Thermonuclear Experimental Reactor (ITER), benchmarks of the transport and of the activation data of tungsten and measurements on a neutronics mock-up of a test blanket module for ITER. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.