Publisher Summary This chapter discusses basic metal cluster reactions. Addition or removal of electrons, the simplest type of chemical reaction, is much more common for transition metal than for main group element compounds. Among the metal complexes, the clusters are predestined for this process. Possible unidentate reagents are atomic cations and other simple electrophiles as well as atomic anions and other simple nucleophiles. All cluster syntheses involve growth or fragmentation of metal atom aggregates. But until very recently, the buildup of clusters or the use of clusters as fragment sources involved empirical approaches with little predictability. The 18-electron rule generally governs the bonding in clusters with up to five metal atoms. Clusters with five, six, and sometimes seven metal atoms can often be treated in terms of skeletal electron counting, describing the frameworks by the nido, closo, and capping formalisms. A systematization of basic cluster reactions has been attempted based on the present status of knowledge. The number of reactions reported is still relatively small for certain reaction types.