C lassical Fourier analysis began withFourier series, i.e., the study of periodic functions on the real line R. Because trigonometric functions are involved, we will focus on 2π -periodic functions, which are determined by functions on [0, 2π ). This is a group under addition modulo 2π , and this group is isomorphic to the circle group T = {z ∈ C : |z| = 1} under the map t → e it . Classical results can be viewed as results on the compact abelian group T, and we will do so.Similarly, Fourier analysis on R n can be viewed as analysis on the locally compact 1 abelian (LCA) group R n . Our general setting will be a locally compact group G. Every such group has a (left) translationinvariant measure, called Haar measure because Alfred Haar proved this statement in 1932. For G = R n , this is Lebesgue measure. Haar measure for G = T is also Lebesgue measure, either on [0, 2π ) or transferred to the circle group T. Haar