Metal cluster chemistry is at the cutting edge between molecular and solid-state chemistry and has therefore had a great impact on the researchers working on organic, coordination, and solid-state chemistry, catalysis, physics, and materials science. The development of new sophisticated synthetic techniques has led to enormous progress in the synthesis of this diverse class of compounds. The number of clusters is growing rapidly, since the possible variations in the metal and ligand sphere are numerous. Modern bonding theories, such as the isolobal principle, have allowed a better understanding of the structures and properties of metal clusters, and thus paved the way for the usage of these versatile materials. Catalysis and nanomaterials are just two of the very promising application-oriented fields.