The requirements defined in the series of European space standards are applicable to all actors working on space projects, but are intended to be viewed from the perspective of a specific project context, and tailored to match the genuine requirements of the project. The project is determined, amongst other things, by its environment, technology maturity, product class, cost and risk constraints, organizational complexity, and the procurement approach adopted for a given acquisition. The tailoring process is carried out by the relevant customer at each level in the hierarchy, in a systematic manner within the rules and constraints of the customer organization, and with due consideration of the engineering, quality and management aspects of the project. The conclusions of the tailoring exercise are incorporated into the project requirements documents. The results of the tailoring decisions by the actor's organization leads to an optimized project implementation process, whereby actors are only constrained by requirements appropriate to their roles and responsibilities in any level within the project hierarchy.