The organophosphonates are biogenic and xenobiotic compounds characterized by the presence of a stable carbon to phosphorus (C-P) bond. The C-P bond imparts upon these molecules a relative resistance to (bio)degradation and fears have been expressed over their environmental recalcitrance and possible ecotoxicity, as more than 20 x 10(3) tonnes of these compounds enter the environment annually in the U.S.A. and western Europe alone (Egli, 1988). Biodegradation of organophosphonates is generally accepted to be dependent upon the phosphate status of the cell, with biodegradation occurring only under conditions of phosphate limitation. In recent years, however, several novel bacteria capable of completely mineralizing both natural and man-made organophosphonates have been isolated. These organisms represent a departure, both at a physiological and genetic level, from the accepted consensus that organophosphonates are utilized only phosphorus sources. This review covers all aspects of our knowledge of organophosphonate metabolism over the last 50 years, concentrating on the advances made in the last 10 years.