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 short and long term), DM changes, pulse broadening, angular extent, and Faraday rotation. Intra-day variable sources (IDVs) are another major topic of the book. Although many variable sources clearly exhibit intrinsic changes, IDVs are generally believed to result from scintillation effects. They require source sizes on the ten micro-arcsec scale, the most extreme cases having profound implications for source lifetimes and emission mechanisms. Finally, a dozen contributions describe future large radio telescope projects, especially the Chinese FAST effort to build a 500 m spherical reflector of innovative design.

The genesis of IAU Colloquium 182, 'Sources and scintillations: refraction and scattering in radio astronomy,' can be traced to the desire, on the one hand, of Beijing Astronomical Observatory radio astronomers to organize a conference which would highlight the need for high sensitivity - as a way ofpromoting their own project to build the world's largest telescope (FAST) - and to a suggestion from Ron Ekers on the other. During a discussion with the two SOC co-chairs (as they then were not) in January 1999 in Epping, Ron noted the success ofa meeting on 'radio seeing' in Beijing in 1989, and wondered whether the time might not be ripe to organize another conference devoted to radio propagation. This set the ball rolling, and with enthusiastic input from SOC members, a successful application was made to the IAU. Later, the URSI also agreed to co-sponsor the meeting. From April 17-21, 2000, over 80 astronomers from a dozen countries met in Guiyang, China, to discuss the latestexciting results and theoretical ideas on radio propagation through interstellar, intergalactic and interplanetary space. These pro ceedings include almost all (95%) ofthe oral presentations given at the conference. In addition to the 52 talks presented during 5 days of the Colloquium, Ron Ekers gave a fine summary at the end to tie things up. There were also poster sessions where some twenty papers were displayed. Besides the scientific sessions, the LOC had organized a program for spouses and otheraccompanying persons.