In aquatic and subsurface environments, microorganisms can mediate the biogeochemical transformation of toxic metal contaminants. These transformations can control the mobility and toxicity of metal ions, and play an important role in affecting contaminant transport and sequestration. In this talk, I will provide an overview of microbe-metal interactions and discuss the redox and complexation reactions that control metal speciation in the environment. Specifically, I will describe how spectroscopic and genetic techniques can be applied to investigate the molecular mechanisms that govern microbial metal transformations.