The contemporary chemist interested in predicting thermochemical properties such as the standard enthalpy of formation has at his disposal a wide selection of theoretical approaches, differing in the range of applicability, computational cost, and the expected accuracy. Ranging from high-level treatments of electron correlation used in conjunction with extrapolative schemes to semi-empirical methods, these approaches have well-known advantages and shortcomings that determine their usefulness in study of particular types of chemical species. The growing number of published computational schemes and their variants, testing sets, and performance statistics often makes it difficult for a scientist not well versed in the language of quantum theory to identify the method most adequate for his research needs. In this book, the experts who have developed and tested many of the currently used electronic structure procedures present an authoritative overview of the tools for the computation of thermochemical properties of atoms and molecules.