After a general introduction, the basic principles of wake-field and
beamcoupling- impedance computations are explained. This includes time domain,
frequency domain, and methods that do not include excitations by means of a
particle beam. The second part of this paper deals with radio frequency bench
measurements of beam coupling impedances. The general procedure of the wire
measurement is explained, and its features and limitations are discussed.Comment: presented at the Proceedings of the CAS-CERN Accelerator School on
Intensity Limitation in Particle Beams, Geneva, Switzerland -2-11 November
201