Using few examples, this document attempts to illustrate the connexions between the physics, the methods both theoretical and experimental used in the collection of data relevant for Nuclear Energy and those of basic Nuclear Physics. The specialisation on themes and subjects imposed by an applicative science certainly generates overall shifts in focus as well as originality in techniques in order to meet the specific needs of the engineer. On the other hand, the contact always remains close with the most fundamental nuclear science which both nourishes, and is nourished by the Nuclear Energy Data enterprise.