This text presents a rigorous and reasonably complete statement of microeconomic theory as it exists today. It starts with a unified treatment of consumers' demand, followed by an exposition of the theory of production as well as costs and profit functions of competitive firms. Market structures are then studied in detail and, finally, a brief introduction to general equilibrium and welfare economics is presented. The book contains many examples, exercises, and illustrations. The method of exposition unifies several approaches to the subject. The treatment of market structure is unique and more detailed than any book on microeconomic theory. Several parts of the book reflect the original research of the authors that has not appeared in book form before. The text attempts to give rigorous foundations to the material presented in intermediate microeconomics textbooks.