Those features of the biology of terrestrial isopods which make them appropriate organisms for assessing sustainability are described. They are very widespread, easily identified and form a dominant component of the soil arthropod macrodecomposer community in many temperate habitats, reaching densities of up to 3000m - 2 in calcareous grasslands. They feed on dead organic material and are key system regulators of the ecosystem functions of decomposition and nutrient recycling. They can be sampled readily by hand, pitfall trapping or extracted from soil by heat and light. They are sensitive to pesticide applications, marked differences in density being found between conventional and organic cultivation regimes. Isopod biomass is higher under no-tillage or minimum tillage regimes which leave crop residues near the soil surface. Isopods tolerate some heavy metals by accumulating them in vesicles in the hepatopancreas. They are thus, potentially useful for monitoring bio-accumulation of such contaminants and can serve as bioindicators of heavy metal pollution.