People pursue their own interests, whatever those interests might be. Some people have interests that are narrow and selfish, others have interests that are broad and altruistic, still others have interests that are somewhere in between. The idea that people are self-interested underpins all of economic analysis and raises two fundamental questions: 1. How do people choose the actions they think will further their own interests? 2. Can the potentially conflicting interests of different people be made to ‘mesh’ in some sort of socio-economic equilibrium? This book is devoted to a detailed study of the first question. Its Companion Volume (Economy-Wide Microeconomics: Equilibrium, Optimality, Applications and Tests) makes a detailed study of the second question.This book begins with the Arrow-Debreu theory of consumer choice. This theory supposes people choose so as to maximize a complete, continuous, transitive, and reflexive binary preference relation over a non-empty and compact choice set, under certainty. The book then studies numerous modifications, relaxations, and generalizations of each of these restrictions - up to and including recent work on Behavioral theories of choice. The study is presented from the Primal, Dual, and Revealed Preference points of view.Consumers are not the only agents in the economy, as Producers are present as well. Starting with the Arrow-Debreu idea that producers choose from a convex production set so as to maximize profit, a study is made of some of the extensions, modifications, and generalizations of this framework that have appeared in the literature. The study is presented from the Primal and Dual points of view.The final chapter in the book provides a link to its Companion Volume. The Chapter indicates how the theories of consumer and producer choice studied here inform answers of the second question posed above.