Different facets of interplay between harmonic analysis and
approximation theory are covered in this volume.  The topics included are
Fourier analysis, function spaces, optimization theory, partial differential
equations, and their links to modern developments in the approximation theory.
The articles of this collection were originated from two events. The first event
took place during the 9^th ISAAC Congress in Krakow, Poland, 5th-9th August
2013, at the section “Approximation
Theory and Fourier Analysis”. The second
event was the conference on Fourier Analysis and Approximation Theory in the
Centre de Recerca  Matemàtica (CRM), Barcelona, during 4th-8th November 2013,
organized by the editors of this volume. All articles selected to be part of
this collection were carefully reviewed.