Arvin Mosier, a leader in Soil Microbiology and Biochemistry research for over three decades retired from the USDA Agricultural Research Service in 2004. In honor of his retirement, this symposium will review different aspects of his contributions to Soil Microbiology and Biochemistry and discuss research frontiers in each area. Most of the topics center on nitrogen and carbon dynamics in soils, with a focus on the production and consumption of gases (nitrous oxide, dinitrogen, nitric oxide, methane, carbon dioxide) that are of importance to soil fertility, water quality, atmospheric chemistry and climate change. Dr. Mosier was also a leader at the interface between basic and applied science and topics related to soil fertility in cultivation systems ranging from dryland corn in the U.S. Great Plains to rice cultivation in India and the development of methodologies to assess greenhouse gas emissions at the national scale will also be covered.