[en] This paper is a forecast that paints four coherent and contrasting paths to achieve carbon neutrality in France in 2050. They aim to articulate the technical and economic dimensions with reflections on the transformations of society that they imply or that they arouse. The following sectors are detailed: those relating to consumption (land use and planning, construction, mobility and food); those which constitute the productive system (agriculture, forest exploitation and industry), those which form the energy supply (gas, cold and heat, biomass, liquid fuels and hydrogen); those that constitute resources (biomass and waste) and carbon sinks. These sectors are also analyzed with regard to their impacts on water, soil, materials and air quality. This book is the result of more than two years of work carried out by the French organization ADEME, in interaction with external partners, in order to inform the decisions to be taken in the years to come. Because the goal is not to propose a political project nor 'the' right trajectory, but to bring together elements of technical, economic and environmental knowledge in order to make people aware of the implications of the societal and technical choices that will lead to the chosen paths