The last major conference on infrared astronomy was the IAU Symposium No. 96 in June 1980. Since then, the discipline has continued to mature and to contribute to all branches of astrophysics. One particular area of growth has been in spectroscopic capabilities at all infrared wavelengths. The purpose of the Symposium in Toledo was to review the scientific questions to be addressed via infrared spectroscopy and to provide, in the proceedings, a useful summary of the field. The sensitivity of infrared spectroscopic observations is still generally limited by detector characteristics or by thermal background radiation. However in recent years improvements in detector technology together with developments in spectroscopic instrumentation have made possible both quite detailed spectroscopy of the brighter members of many classes of galactic sources and also begun to open up some infrared spectroscopy of extragalactic sources. The potential of the field in the next decade or two is clear. The lRAS mission has completed one of the pre-requisites, namely an all-sky photometric survey. Major space missions utilising cryogenic infrared telescopes have been approved in Europe (ISO) and seem likely in the USA (SIRTF); plans for space submillimeter telescopes are firming up. On the ground large telescopes optimized for infrared observations are now in operation at high altitude sites and specialized submillimeter facilities are under construction. The particular advantages of planned, very large telescopes for infrared observations are widely accepted.

Galactic and Extragalactic Radio Astronomy is a fundamental text for graduate students and professional astronomers and covers all aspects of radio astronomy beyond the solar system. Each chapter is written by a renowned expert in the field and contains a review of a particular area of radio astronomy and presents the latest observations and interpretations as well as an extensive view of the literature (as of 1988). Topics covered include: galactic continuum emission, HII regions, the diffuse interstellar medium, interstellar molecules, astronomical masers, neutral hydrogen, the galactic center, radio stars, supernova remnants, pulsars, extragalactic hydrogen, radio galaxies and quasars, the microwave background, and cosmological radio sources.

The previous Saas-Fee Advanced Course dedicated to the interstellar medium took place in 1972. The tremendous scientific advances that have occurred in this field since then, in particular owing to the availabihty of receivers working at completely unexplored wavelength bands, fuUy justified a new set of lectures. As a consequence, the members of the Swiss Society for Astrophysics and As tronomy voted that "The Galactic Interstellar Medium" should be the subject of the 1991 course. The 21st Saas Fee Advanced Course took place in Les Diablerets from 18 to 23 March 1991, gathering together about 80 participants from all over the world, but mostly from Europe. According to a rule that has proved to lead to success, but also to chal lenge the lecturers' energy, the format of a Saas-Fee Advanced Course consists traditionally of 28 lectures of 45 minutes which take place in the morning and late afternoon, leaving ample time for discussions, self-study, hiking or skiing. Despite the inordinate work load imposed, this year's lecturers felt that the subject was sufficiently dense to increase the lecture time by 1/3! This proved judicious and left more time for questions and discussions during the lectures.

This new, fourth, edition of Allen's classic Astrophysical Quantities belongs on every astronomer's bookshelf. It has been thoroughly revised and brought up to date by a team of more than ninety internationally renowned astronomers and astrophysicists. While it follows the basic format of the original, this indispensable reference has grown to more than twice the size of the earlier editions to accommodate the great strides made in astronomy and astrophysics. It includes detailed tables of the most recent data on: - General constants and units - Atoms, molecules, and spectra - Observational astronomy at all wavelengths from radio to gamma-rays, and neutrinos - Planetary astronomy: Earth, planets and satellites, and solar system small bodies - The Sun, normal stars, and stars with special characteristics - Stellar populations - Cataclysmic and symbiotic variables, supernovae - Theoretical stellar evolution - Circumstellar and interstellar material - Star clusters, galaxies, quasars, and active galactic nuclei - Clusters and groups of galaxies - Cosmology. As well as much explanatory material and extensive and up-to-date bibliographies.

This new fourth edition of Allen's classic Astrophysical Quantities belongs on every astronomer's bookshelf. It has been thoroughly revised and brought up to date by a team of more than ninety internationally renowned astronomers and astrophysicists. While it follows the basic format of the original, this indispensable reference has grown to more than twice the size of the earlier editions to accommodate the great strides made in astronomy and astrophysics. It includes detailed tables of the most recent data on: - General constants and units - Atoms, molecules, and spectra - Observational astronomy at all wavelengths from radio to gamma-rays, and neutrinos - Planetary astronomy: Earth, planets and satellites, and solar system small bodies - The Sun, normal stars, and stars with special characteristics - Stellar populations - Cataclysmic and symbiotic variables, supernovae - Theoretical stellar evolution - Circumstellar and interstellar material - Star clusters, galaxies, quasars, and active galactic nuclei - Clusters and groups of galaxies - Cosmology. As well as much explanatory material and extensive and up-to-date bibliographies.