Microbial degradation of toxic organic chemicals and transformation of metal pollutants are important naturally occurring processes.However to evaluate and predict the importance of these processes in protecting human and environmental health there is a need for an environmental systems perspective on dynamic control of biodegradation and the ultimate efficacy of the engineered process in bioremediation technology.Most organic pollutants are subject to biodegradation.However,it is well known that those chemicals of synthetic industrial origin,high molecular weight polymeric chemicals,highly oxidized or halogenated chemicals,and those of limited solubility are notoriously difficult to degrade and typically pose site specific challenges for effective bioremediation.New molecular biology tools are now available to complement classical microbiological and biochemical insight into the ecology and engineering potential for bioremediation of pollutants ranging from TCE,PCB and DIOXIN to Poly Aromatic Hydrocarbons and Crude Petroleum.When coupled to a system science perspective it is possible to better predict success and failures of bioremediation,and identify control points that may help to optimize these naturally occurring processes.