This classic text reads as well now as it did 15 years
ago when I read it as graduate student. Should be accessible
to better undergraduates but everyone interested in mathematics
can take pleasure in this presentation of a wide variety of topics
in basic Fourier theory together with interesting applications.
But note that this book is not an introduction to current research
in harmonic analysis. For that one should look at books by Stein
and others. Nonetheless, this is a beautiful introduction the
basic theory.