Very recently it has become possible to produce and characterize large clusters containing an exact, predetermined number of atoms. Through these efforts it has become clear that clusters containing even as many as 20,000 atoms cannot yet be considered as being tiny crystals. Their structure is often icosahedral. Their electrons are organized into shells rather than bands. In many respects the clusters behave more like giant atoms than solids. Only a few groups have begun to develop the experimental and theoretical techniques needed for the study of clusters containing 100 or more atoms. In this work, representatives from these groups have contributed tutorial chapters explaining the methods they have developed.