The course is focused on the principles and applications of stable and radiogenic isotope geochemistry to understanding geological and planetary processes. The course will be taught using specific case studies from selected themes, which will change on a yearly basis. Possible themes might include: early solar system chronology, isotopic contraints on Earth differentiation, tracing pollutants in the subsurface, nature of the early Earth, ocean and atmospheric circulation, applications to tectonics. The course will be team taught, in which individual instructors will focus on a particular aspect of each theme, providing some lectures for background prior to reading the important literature.