First published in 1968, An Introduction to Harmonic Analysis has firmly established itself as a classic text and a favorite for students and experts alike. The book has withstood the test of time and earned Professor Katznelson the 2002 Leroy P. Steele Prize for Mathematical Exposition. Starting with a clear presentation of classical Fourier series, the aim of the book is to demonstrate the central ideas of harmonic analysis in a concrete setting and to provide a stock of examples to foster a clear understanding of the theory. Once these ideas are established, the author goes on to show that the scope of harmonic analysis extends far beyond the setting of the circle group, and he opens the door to other contexts by considering Fourier transforms on the real line as well as a brief look at Fourier analysis on locally compact abelian groups. This new edition has been revised by the author and offers some additional material, including topics from approximation theory and examples of the use of probabilistic methods in harmonic analysis. Yitzhak Katznelson received his Ph.D. from the University of Paris. He is currently a professor of mathematics at Stanford University. He has also taught at the University of California, Berkeley; Hebrew University; and Yale University. His mathematical interests include harmonic analysis, ergodic theory, and differentiable dynamics.