The first part of this book contains the material for a course in standard microeconomics and general equilibrium. These chapters contain the necessary background on commodities, consumers, producers, as well as the classical results about the existence of general (Walras) equilibria and the fundamentals of welfare theory. The second part of the book may be seen as a continuation dealing with more advanced topics.This textbook shows how the general equilibrium theory can be put into use to provide new insights into various fields of economic science. The reader does not need previous particular mathematical training; the formal approach is introduced in a piecemeal fashion, so that no difficult mathematics occurs in the beginning.