Modern particle accelerators and storage rings, whether used for high-energy physics, synchrotron light sources, or other purposes, require particle beams with the highest possible intensity. In order to achieve this maximum performance, a good understanding of the interaction of the charged particle beams with the surrounding vacuum chamber and other accelerator components is necessary. In the frequency domain, this interaction can be described by impedances, and equivalently by wake fields in the time domain. These need to be known to estimate the thresholds of coherent instabilities, or...