In electrogenerated chemiluminescence, also known as electrochemiluminescence (ECL), electrochemically, generated intermediates undergo a highly, exergonic reaction to produce an electronically excited state that then emits light. These electron-transfer reactions are sufficiently exergonic to allow the excited states of huminophores, including polycyclic aromatic hydrocarbons and metal complexes, to be created without photoexcitation. For example, oxidation of [Ru(bpy)(3)](2+) in the presence of tripropylamine results in light emission that is analogous to the emission produced by photoexcitation. This review highlights some of the most exciting recent developments in this field, including novel ECL-generating transition metal complexes, especially ruthenium and osmium polypyridine systems; ECL-generating monolayers and thin films; the use of nanomaterials; and analytical, especially clinical, applications.