The PACT project aims at shaping what a sustainable post-carbon society would look like and how we could reach it within the next 50 years. It will focus first on what shape the energy demand, and how this should evolve towards post-carbon concept, from two viewpoints: that of the infrastructures, in relation to urbanisation and land-use schemes, and that of the life-styles and behaviours, in relation to the technologies that should be available. It will then deepen the question of urbanisation and land-use from the renewable energy perspective, including that of the systems (centralised/dependence versus decentralised/autonomous). Last, PACT will investigate the role of social forces, actors, stakeholders in the transition process toward this post-carbon concept. The ultimate objective of the project is to complement these analytical components with an attempt to quantify scenarios of post-carbon societies, at the world level.