To understand the environmental behavior of metals we must consider a tremendous range of phenomena, from simple individual reactions, such as ligand complexation and solubility equilibria, to quite complicated and collective processes, such as metal-mineral-microbial interactions. Because of pressing contamination problems at DOE sites and the paucity of relevant actinide chemistry knowledge, research is needed in this entire range of science. The determination and evaluation of key thermodynamic data for actinide species and the development of geochemical, hydrological, and environmental transport models are progressing. In contrast, we know almost nothing about how actinides interact with microorganisms. Ubiquitous microorganisms can absorb, reduce, oxidize, solubilize, or precipitate actinides, thereby affecting their speciation, solubility, bioavailability, and migration. These effects are due to both direct and indirect interactions, such as sorption to the cell wall and reaction with microbial byproducts, respectively. Our goal is to fully characterize specific microbial-actinide interactions, both to develop this area of fundamental research and to determine how the interactions may be exploited to affect environmental actinide mobility/immobility and remediation efforts. ©2000 American Institute of Physics.