The theories and techniques that underlie the advances of radio interferometry as applied to astronomy and astrometry, continue to evolve but have reached a sufficient state of maturity that it is appropriate to offer a detailed exposition. It is the aim of the authors to explain the underlying principles of the relevant interferometric techniques but to limit the discussion of details of implementation. This book is intended primarily for graduate students and professionals in astronomy, electrical engineering, physics, or related fields who wish to use interferometric or synthesis-mapping techniques in astronomy, astrometry, or geodesy. It is also written with radio systems engineers in mind and includes discussions of important parameters and tolerances for the types of instruments involved.