This chapter presents a straightforward discussion of the chemistry of carboxylic acids (formerly called “fatty acids”) and nitriles. As usual, we begin with a description of how the compounds are named. We then consider the subtleties of their structure, and how these structural features influence physical properties, such as boiling point. We place considerable emphasis on the dissociation of carboxylic acids and the effect of substituents on acid strength. We have already encountered a number of methods of preparing carboxylic acids. We shall review these methods, and learn about two additional procedures. The only reactions of carboxylic acids that we study in detail in this chapter are reduction and decarboxylation, although two other common reactions of carboxylic acids, alpha substitution and nucleophilic acyl substitution, will be described in later chapters. We will then look at the formation of nitriles and their chemical reactivity; and our discussion of carboxylic acid and nitrile chemistry concludes with a look at the infrared and NMR spectra of these compounds, with emphasis on the characterization of carboxylic acids. 4.2.1: Chapter Objectives and Introduction to Carboxylic Acids 4.2.2: Naming Carboxylic Acids and Nitriles 4.2.3: Structure and Properties of Carboxylic Acids 4.2.4: Reactions of Carboxylic Acids - An Overview 4.2.5: Chemistry of Esters 4.2.6: Chemistry of Amides