: This paper proposes a development process for interactive systems based both on verification and validation methods. Our approach is formal and use at first the B Method. We show in this paper how formal B specifications can be derived from informal requirements in the informal notation UAN. Then, these B specifications are validated using the data oriented specification language EXPRESS. Several scenarios can be tested against these EXPRESS specifications. Key words: B Method, EXPRESS, UAN, interaction properties, verification, validation, formal specification of interactive systems.