The field of application of Function Analysis has evolved from its first application to become, today, an effective support for any kind of project (or product), accompanying any process of definition and development of an action. This document is applicable in principle to all sectors of activity and to all types of projects or products, tangible or intangible, for example, services, processes, organizations, strategies, tactics, goals and objectives. It is applicable in the context of relations between external partners (between a client and its suppliers) or internally (between two entities of the same organization for example). The objective of any professional activity, private or public, is to be able to offer its internal or external customers, and users an efficient and competitive offer. The product can be any kind of system or service, of any complexity, over all or part of its life cycle (and beyond). The product should meet an identified need, which constitutes the basis for a concerted development by internal and/or external partners. The goal is to have the best proposal that meets the expectations of the various customers, users and other selected stakeholders involved. This standard constitutes a reference document for any actor wishing to deploy or have to implement Function Analysis (Initiator may be at any level in the organization, anyone involved in any product definition or operating conditions during its complete life cycle). It is also intended for anyone who wants to understand the issues and benefits of using this mode of work in order to advocate for it. This standard also sets out the rules and conditions for the implementation of the approach and associated methods and provides trainers with a solid framework for teaching them. The Function Analysis approach can be implemented with benefits in all types of organizations, including enterprises. Function Analysis can also be used to conduct personal reflection for tasks of any size and nature. To present the conditions for its implementation and development, the document: specifies the interests and areas of application of the Function Analysis; presents the variety of situations in which Function Analysis is used in different fields of application for its implementation, in support of projects of all types and sizes; outlines the methods, associated requirements, and tools for its implementation: functional Needs Analysis (support for the process of defining the objectives and the goal to be achieved); technical Functional Analysis (support for design or research processes and evaluation of solutions) and their combined operations; the process (FNA and TFA), creative in nature, can be, in accordance with the stated objectives, sometimes iterative to develop the best proposal; for the Functional Need Analysis (FNA), the standard sets out FNA requirements for the results (deliverables) expected from its implementation to establish the Functional Need Expression (FNE). These can serve as a basis for establishing an understanding of the overall needs of the market, the characterized representation of service functions, constraints and interfaces, an assessment of the changes made, whether or not the needs are under control, and to support the choice of solutions and the verification of the chosen solution. These deliverables can also serve as a basis for writing, characterizing functional interfaces, conducting preliminary risk and reliability studies, conducting economic studies such as costs/impacts of functions, etc., and, if applicable, write a Functional Performance Specification (FPS); for Technical Function Analysis (TFA), the standard sets out the requirements for the expected results (deliverables) of the Technical Function Analysis approach. These will be used to establish, for example, function diagrams, function tree charts, tree charts of technological pathways, for assigning delivery elements to functions, costs per function, and other relevant allocations for decisions to be instructed to establish the most effective solution. In addition, the process is based on methods that should be adapted according to the size and maturity of the product studied, the challenges related to its development and operation, and the available resources. Function Analysis will be all the more effective as it will intervene early ( anticipating in the projects). Additionally, European Union (EU) directives such as the EU Public Procurement Directive 2014/24 and update notices, have also encouraged the market in the wider use of the Functional Performance Specification. NOTE 1 Function Analysis actions and reflections according to its principles constitute an essential basis and support for any Value Analysis, Value Engineering or Value Management action (standard EN 12973:2020). NOTE 2 A specific use of the concepts and requirements defined in this document with the objective of establishing a Functional Need Expression and a Functional Performance Specification resulted in the development of a particular standard EN 16271:2012.