[en] The following notes were intended as complement to the main topic of the lectures presented at the Winter College on Nuclear Physics and Reactors. Actually, the topic was covered according to the outline given in Appendix and the presentation was based as far as possible on the practical features of the basic data file, in particular the ENDF/B files. The present notes are subdivided in two parts; part I is a general introduction to the problem of the evaluated data files and gives the main references on the topic. Part II presents a few specific examples of the use of the evaluated data files in the wide application fields of neutron heating and photon production