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: states the interests and fields of application of the Functional Need Analysis, Functional Need Expression and Functional Performance Specification concepts; determines the contents requirements of the functional need expression structured in four main bodies: global definition of the need; definition of the strategic elements and the consolidation of needs; highlighting of principles, and concepts chosen beforehand, if any; description of the functions to be provided and of the constraints to be complied with. determines the requirements on the composition and contents of a functional performance specification and those used to assess its quality, i.e. requirements concerning: its contents and structure; the assessment of the characteristics which define its quality. precisely specifies, in the form of requirements: the conditions for a successful Functional Need Analysis (FNA) action producing a deliverable called Functional Need Expression (FNE); the conditions for drawing up a successful functional performance specification (FPS) based on the available functional need expression (FNE); the conditions of use of the FPS by the inquirer and the various partners involved (the provider for example); specifies the various conditions of use of these concepts.This European Standard is applicable in principle to all product types and dimensions (from the elementary tangible object to the definition of an organisation and its strategy, including the systems or processes and activities implemented by an organisation) and to all sectors of activity (including the service sector). Lastly it is applicable within the framework of relationships between external partners (between a customer and its providers) or internally (between two entities of the same organisation for example).