Intrinsic bioattenuation has recently evolved as a viable remediation alternative at a number of sites where the risk of exposure to contaminants is within acceptable standards. Important mechanisms controlling the instrinsic bioattenuation include advection, dispersion, sorption, dissolution from a residual source, and abiotic and biological transformations. Since intrinsic bioattenuation is a plume management strategy, it requires characterizing and monitoring these processes. Intrinsic bioattenuation involves an assessment of risks to public health and the environment, and consequently requires prediction of the fate and transport of contaminants at the candidate sites. This paper reviews the processes controlling intrinsic bioremediation and summarizes case histories where intrinsic bioattenuation has been observed at sites contaminated with petroleum hydrocarbons and chlorinated solvents. The key steps in evaluation natural attenuation as a remedial alternative are summarized.