The adaptation of agriculture and forestry to the climate of the twenty-first century supposes that research projects will be conducted in cooperative actions between meteorologists, agronomists, pedologists, hydrologists, and modellers, ... To prepare for it, it is appropriate first of all to study the variations in the climate of the past using extensive, homogenised series of data (meteorological, phenological, etc.). General circulation models constitute the basic tool for forecasting the future climate. They may still be improved, and the regionalisation techniques used for downscaling climate predictions could also be made more efficient. The crop simulation models using input data from the general circulation models applied at the regional level ought to be the favoured tools which allow the extrapolation of the major trends on yield, consumption of water, fertiliser, pesticides, the environment and rural development. For this, they have to be validated according to the available agronomical data, particularly the available phenological series on cultivated crops. In addition, a climatic change would have a certain impact on crop diseases and parasites, as well as on weeds. Very few studies have been carried out in this field. It is also necessary to quantify the stocks and fluxes of carbon in the large forest ecosystems, simulate their future, and assess the vulnerability of the various forest species. This is all the more important in that some choices of species must be made in the course of the next ten years in plantations which will experience the climate of the end of the twenty-first century. More broadly speaking, we shall have not only to try hard to research new agricultural and forestry practices which will reduce greenhouse gas emissions by agriculture and / or promote the storage of carbon, but it will also be indispensable to prepare the adaptation of numerous rural communities for the climatic changes (particularly those in the South countries