A comprehensive review of Ru(ll) complexes with α-diimine chelating ligands containing flve-membered heterocyclic moieties is presented. The discussion focuses on the spectroscopic (NMR, electronic absorption, and emission), electrochemical, and photochemical aspects of homoleptic and heteroleptic metal complexes, with a brief presentation of related polymetallic compounds. Particular emphasis is given to the comparison with polypyridyl analogues, as well as to the large variation on the properties of the resulting complexes brought about by the introduction of azole (imidazole, pyrazole, triazole, oxazole, thiazole, selenazole, and thiadiazole) moieties.