Recent years have seen a rapid growth in the interest of heterometallic complexes. Numerous researchers are now actively developing synthetic approaches to heterometallic complexes, studying their properties, and developing their applications as catalysts. One particular area of promise is heterometallic complexes that contain direct metal-metal bonds. The study of these types of complexes and their mechanisms of action, brings with it new fundamental questions about ligand exchange events. For single-site metal complexes, the processes involved in ligand exchange are well described and typically involve associative, dissociative, or interchange pathways. These steps are fundamentally important in catalysis since they underpin substrate binding and product release from the active site. The proximity of two, bonded, metal centres bring with them new possibilities for intramolecular ligand exchange processes that involve the migration of ligands from one metal site to the other. These include: (i) 1,2-migration of a ligand from one metal to the other, (ii) double 1,2migration of two ligands from one metal to the other, and (iii) dyotropic rearrangement of two ligands in which they switch position between the two metals (Scheme 1). Scheme 1. Metal to metal ligand migration pathways in bimetallic systems: (i) 1,2-migration; (ii) double 1,2migration; (iii) dyotropic 1,2-migration.