Climate is the most important component of the Earth's environment and climatic fluctuations have a strong impact on water supplies, vegetation, energy use etc. Thus our understanding of the climatic system is of utmost importance. Leading experts in the field of climate modelling and paleoclimatology present the most recent methods for reconstructing past climatic variations and for modelling the climatic system and its evolution. The first of three parts is devoted to the climatic system and the physical basis for its modelling; the second summarizes the evolution of the global atmosphere, the ocean, the continents, the biosphere, and the ice sheets during recent climatic cycles; the last part focusses on the understanding of past and future climatic changes.