In industrialised services activities designed for customers, the success of the innovation depends on, besides the traditional factors used, the way the customer deals with the innovation, all the more so when the innovation introduced has modified the tasks conferred upon him in the service production process. In these conditions, how can the validation of innovation by the customer from concept definition to the implementation of the evaluation methods be integrated? This article first discusses theoretical works in project management to answer this question for service innovation projects. The basis for the analysis is a series of three case studies of French services firms. It underlines the diversity of solutions used by firms. This preliminary research makes two methodological points. First, it presents different ways of identifying the stages in which these problems can be solved. Second, it clarifies what should be validated at each stage, and which factors determine the methods and the necessary resources to carry them through.