Among the strategies supporting the reactivity of companies, the development of actors’ versatility holds a promising place. In this article, we present multi-periods planning and scheduling of projects, with the problem of workforce allocation, taking into account two dimensions of flexibility. The first is the modulation of working time, which provides the company with considerably fluctuating work capacities for a given manpower. The second flexibility lever is the versatility of operators: for all the actors who can prove to be multi-skilled, we adopt a dynamic vision of their competences. This model takes into account the evolution of their skills over time, depending on how much they have been put in practice in previous periods. In this approach, the durations of activities are not known in advance, and rely on the productivities of the solicited actors – and thus on their previous allocations. We present the characteristics of this problem, and a solving approach based on genetic algorithms.