Bioremediation can be defined as any process where biological agents provide a practical solution to the unwanted presence of a chemical substance. In providing this solution, the risk or probability that a hazard may act must be substantially reduced. Thus, in its broadest sense, even the introduction of GM technology to reduce dependence on insecticides (Fitt, 2000), or the encouragement of beneficial predators of pests could be included in bioremediation. However, in this paper the term will be restricted to processes where a more specific biological agent, usually a microbe or microbial product or a plant is recognised as reducing the risk from agrochemicals such as insecticides or herbicides. In particular, attention will be directed towards those processes acting to reduce the 'half-life' of the chemical as a contaminant in the local environment. The half life is the time taken for the amount of chemical present to be reduced to half a baseline value. The term remains very broad though, since a range of physical or chemical actions mediated by these biological agents could be involved in reducing the amount of the chemical present.