  Power coupling is the subject of a huge amount of literature and material
since for each particular RF structure it is necessary to design a coupler that
satisfies some requirements, and several approaches are in principle possible.
The choice of one coupler with respect to another depends on the particular RF
design expertise. Nevertheless some 'design criteria' can be adopted and the
scope of this paper is to give an overview of the basic concepts in power
coupler design and techniques. We illustrate both the cases of
normal-conducting and superconducting structures as well as the cases of
standing-wave and travelling-wave structures. Problems related to field
distortion induced by couplers, pulsed heating, and multipacting are also
addressed. Finally a couple of design techniques using electromagnetic codes
are illustrated. The paper brings together pictures, data, and information from
several works reported in the references and I would like to thank all the
authors of the papers.
