The only authoritative reference source on the propagator concept, now thoroughly revised and updatedMuch has changed in the study of quantum and theoretical chemistry since the publication of the first edition of Propagators in Quantum Chemistry. Advances in computer power and software packages now make it possible to calculate molecular structure, properties, spectra, and reactivity with greater predictive power. Chemical processes, especially under conditions not readily available in the laboratory, can also be much more easily studied via theory and computations..