The objective of this thesis is to extend the formal methodology of re.nement of requirements specifications SCTL/MUS to a multi-perspective environment where coexist requirements speci.cations which belong to each stakeholder involved in the software development of the system. To reach this goal, the new methodology (referred to as X-SCTL/MUS) bets on using a viewpoint-based approach which allows to gather and maintain (possibly inconsistent and incomplete) information gathered from multiple sources. It explicitly separates the descriptions provided by different stakeholders, and concentrates on identifying and resolving conflicts between them.