This European Standard is a tool to be used by any partner wishing to draft and make use of the reference of any need to be satisfied. In light of this purpose, it: a) states the interests and fields of application of the Functional Need Analysis, Functional Need Expression and Functional Performance Specification concepts; b) determines the contents requirements of the functional need expression structured in four main bodies: 1) global definition of the need; 2) definition of the strategic elements and the consolidation of needs; 3) highlighting of principles, and concepts chosen beforehand, if any; 4) description of the functions to be provided and of the constraints to be complied with. c) determines the requirements on the composition and contents of a functional performance specification and those used to assess its quality, i.e. requirements concerning: 1) its contents and structure; 2) the assessment of the characteristics which define its quality. d) precisely specifies, in the form of requirements: 1) the conditions for a successful Functional Need Analysis (FNA) action producing a deliverable called Functional Need Expression (FNE); 2) the conditions for drawing up a successful functional performance specification (FPS) based on the available functional need expression (FNE); 3) the conditions of use of the FPS by the inquirer and the various partners involved (the provider for example); e) specifies the various conditions of use of these concepts.