The Plancherel formula says that the L^2 norm of the function is equal
to the L^2 norm of its Fourier transform. This implies that at least
on average, the Fourier transform of an L^2 function decays at
infinity. This book is dedicated to the study of the rate of this decay
under various assumptions and circumstances, far beyond the original
L^2 setting. Analytic and geometric properties of the underlying
functions interact in a seamless symbiosis which underlines the wide
range influences and applications of the concepts under consideration.