The process of establishing the services that the customer requires from a system and the constraints under which it operates and is developed Row requirements need to be categorized in: Functional requirements describe system services functions\ Non functional requirements is a constraints on the system or on the development process It may range from a high level abstract statement of a service or of a system constraint to a detailed mathematical functional specification This is inevitable as requirements may serve a dual function May be the basis for a bid for a contract - therefore must be open to interpretation May be the basis for the contract itself therefore must be defined in detail both these statements may be called requirement