1. Abundance and Measurement of Stable Isotopes. 1.1. Discovery of Isotopes. 1.2. Nuclide Types, Abundances, and Atomic Weights. 1.3. Properties and Fractionation of Isotopic Molecules. 1.4. Material Balance Relationships. 1.5. Mass Spectrometers. 1.6. Notation and Standards. 1.7. Summary. 1.8. Problems. References. 2. Isotopic Exchange and Equilibrium Fractionation. 2.1. Isotopic Exchange Reactions. 2.2. Basic Equations. 2.3. Molecular Models. 2.4. Theory of Isotopic Fractionation. 2.5. Temperature Dependence of Isotopic Fractionation Factors. 2.6. Rule of the Mean. 2.7. Isotopic Thermometers.