This book will give students a thorough grounding in pH and associated equilibria, material absolutely fundamental to the understanding of many aspects of chemistry. It is, in addition, a fresh and modern approach to a topic all too often taught in an out-moded way. This book uses new theoretical developments which have led to more generalized approaches to equilibrium problems; these approaches are often simpler than the approximations which they replace. Acid-base problems are readily addressed in terms of the proton condition, a convenient amalgam of the mass and charge constraints of the chemical system considered. The graphical approach of Bjerrum, Hägg, and Sillén is used to illustrate the orders of magnitude of the concentrations of the various species involved in chemical equilibria. Based on these concentrations, the proton condition can usually be simplified, often leading directly to the value of the pH. In the description of acid-base titrations a general master equation is developed. It provides a continuous and complete description of the entire titration curve, which can then be used for computer-based comparison with experimental data. Graphical estimates of the steepness of titration curves are also developed, from which the practicality of a given titration can be anticipated. Activity effects are described in detail, including their effect on titration curves. The discussion emphasizes the distinction between equilibrium constants and electrometric pH measurements, which are subject to activity corrections, and balance equations and spectroscopic pH measurements, which are not. Finally, an entire chapter is devoted to what the pH meter measures, and to the experimental and theoretical uncertainties involved.