For organometallic compounds, there are a number of characteristic reactions and most of them involve 1e donor ligand(s). Understanding of these reactions is very important to master organometallic chemistry. This chapter explains several basic examples among the many characteristic reactions of organometallic complexes. Oxidative addition refers to the reaction in which a compound (A–B) having a covalent bond between A and B reacts with a transition metal fragment described as L_nM (L generally stands for a supporting ligand) to give L_nM(A)(B), where A and B are new ligands at the metal. Since this reaction is formally reversible, it may be written as an equilibrium. The reverse reaction is referred to as reductive elimination. C–H and C–C bond cleavage and C–C bond formation, which are important in organic chemistry, are achieved by oxidative addition reaction and reductive elimination, and are reactions characteristic of organometallic chemistry. Another pair of typical reactions is insertion and elimination. For a transition metal complex having, for example, hydride, alkyl or aryl ligands, other molecules may insert into the M–H or M–C bond. Two typical types of insertion reactions, insertion of CO and olefins, are described in detail. The reverse reactions are β hydride elimination and β alkyl elimination, respectively.