One of the major challenges of science in the last few years of the second millennium is learning how to design materials which can fulfill specific tasks. Ambitious as it may be, the possibilities of success are not ne~li~ble provided that all the different expertises merge to overcome the limits of e XIsting disciplines and forming new paradigms science. The NATO Advanced Research Workshop on "Magnetic Molecular Materials" was organized with the above considerations in mind in order to determine which are the most appropriate synthetic strategies, experimental techniques of investigation, and theoretical models which are needed in order to develop new classes of magnetic materials which are based on molecules rather than on metallic or ionic lattices. Why molecules? The answer may be obvious: molecular chemistry in principle fine can tune the structures and the properties of complex aggregates, and nature already provides a large number of molecular aggregates which can perform the most disparate functions. The contributions collected in this book provide a rather complete view of the current research accomplishments of magnetic molecular materials. There are several different synthetic approaches which are followed ranging from purely organic to inorganic materials. Some encouraging successes have already been achieved, even if the critical temperatures below which magnetic order is observed still are in the range requiring liquid helium.