The topics covered in this book include: theory of scattering and scintillation, distribution of scattering material, intra-day variability, pulsars and their magnetospheric structure, polarization of AGN, interplanetary scintillation, and future highly-sensitive radio telescopes. The introductory papers emphasize the essential properties of diffractive and refractive scattering, how they differ in temporal and frequency structure, and what they reveal about irregularities in the ISM. Pulsars can be examined in a number of different ways as a function of frequency: time variability (both...