This course is a quantitative exploration of isotopic systems in the environment. We will go beyond the introduction of basic isotope geochemical concepts and focus on the calculations and considerations necessary for using isotopes as tools for answering a variety of science questions. Examples will be taken from ecology, archaeology, physiology, climatology, and geology. Students will learn the physical theory behind fractionation and be able to plan and interpret results of isotope tracer experiments through basic calculations and box modeling. The majority of the examples will be from stable isotopes, but we will also spend some time with radioactive isotopes and their application in studying natural systems. This course is designed for the student who has some experience already with the basic concepts in isotope geochemistry and is ready to take it to the next level to practice using those basic concepts quantitatively. Students will gain practical experience through weekly problem sets. Periodic exams throughout the semester will be used to assess student learning, with a final exam at the end. Prerequisite: MEES 626 or permission of instructor.