This book offers a broad discussion of the concepts required to understand the thermodynamic stability of molecules and bonds and a description of the most important condensed-phase techniques that have been used to obtain that information. Above all, this book attempts to provide useful guidelines on how to choose the best data and how to use it to understand chemistry. Although the book assumes some basic knowledge on physical-chemistry, it has been written in a textbook style and most topics are addressed in a way that is accessible to advanced undergraduate students. Many examples are given throughout the text, involving a variety of molecules. This text will provide a good starting point for those who wish to initiate in the field or simply to understand how to assess, to estimate, and to use thermochemical data. It will therefore appeal to a broad range of practicing chemists and particularly to those interested in energetics-structure-reactivity relationships.