Owing to their fairly high stability under visible irradiation, ferrocene and ferrocenyl derivatives are widely used in luminescent systems. They are classical quenchers of excited states. Both energy and electron transfer may be involved, depending on the nature of the excited species. Inter- or intramolecular quenching are encountered. Applications span from the study of reaction mechanisms to that of organized or biological media. Recently, dyads and polyads designed for their ability to mimic photosynthetic centers or for their photodiode properties have also been obtained. Finally, the incorporation of a ferrocenyl derivative in a luminescent system does not necessarily lead to luminescence quenching. New applications are emerging, in which advantage is taken of the presence of ferrocene acting as a redox center: this gives optically and electrochemically active sensors. The present review encompasses the literature up to November 1999.