Radio astronomy uses unique observational techniques and offers the only way to investigate many phenomena in the Universe. This book, by two founders of the field, presents both a clear introduction to radio telescopes and techniques, and a broad overview of the radio Universe. The material in this new edition has been expanded and updated, reflecting the developments in the field over the last decade. The first half of the book includes reference material on the fundamentals of astrophysics and observing techniques, describing how radio telescopes work - from basic antennas and single aperture dishes through to full aperture-synthesis arrays. New material reflects the increasing use of aperture synthesis and very-long-baseline interferometry, and the further exploitation of molecular spectral lines. A new chapter is devoted to the fundamentals of radiation and propagation theory. The second half of the book constitutes a review of radio observations of our milky Way galaxy, stars, pulsars, radio Galaxies, quasars and the cosmic microwave background. Reviews of Fourier transform theory, celestial coordinate systems and a historical outline of the subject are provided in appendices. Wide-ranging and clearly written, this book provides a thorough and up-to-date introduction to the subject for graduate students, and an invaluable overview for researchers turning to radio astronomy for the first time.