1) Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA, 2) Department of Chemistry, University of Rochester, Rochester, NY 14627, USA Earth and Planetary Science Letters (2004), V217, pp223-236, doi: 10.1016/S0012-821X(03)00572-7 Iron stable isotopes: beyond biosignatures A.D. Anbar (1,2) The stable isotope geochemistry of Fe has attracted intense interest in the past five years. This interest was originally motivated by the possible use of Fe isotopes in biosignature applications, particularly in sediments from the ancient Earth or Mars. This application is still being developed, with particular attention to fractionation mechanisms. Understanding such mechanisms should also provide new insights into the environmental biogeochemistry of Fe. At the same time, the Fe isotope system holds promise for other exciting frontiers, including applications in oceanography, solid Earth geochemistry and biomedicine. Such applications will be increasingly attractive as Fe isotope analysis becomes routine.