This course is an introduction to the application of stable and radiogenic isotopes to Biogeochemistry, Environmental Science, Ecology and Paleo-ecology. The primary emphasis will be on the applications of light and "non-traditional" stable isotopes, with a smaller emphasis placed on the application of radiogenic isotopes. The course will begin with the theory, nomenclature and methods of isotope analysis. This will be followed by applications of: H and O isotopes in the atmosphere and in paleo-thermometry; C, N and S isotopes in plants, foodwebs, soils and oceans; "non-traditional" isotopes such as Fe, Ca and Hg in the growing range of Earth surface studies; and the application of radiogenic isotopes as fingerprints of contaminant and nutrient sources.