Introducing the application of free energy correlations to elucidating the mechanisms of organic and bio-organic reactions, this volume provides a new and illuminating way of approaching a potentially complex topic. The idea of how free energy correlations derive from polar substituent change is introduced, and common pitfalls encountered in the application of free energy relationships are described, along with the use of these anomalies in mechanistic studies. The concept of effective charge is described in detail, with examples of its application. Throughout, worked answers are provided for the problems posed and databases of parameters, and comprehensive lists of further reading are also included.