The book is the first monograph in the world literature devoted to the problems of a new branch of science - radio astrometry, which arose at the junction of radiophysics and astrometry. The book considers new ways to solve the fundamental problems of astrometry and related sciences (geodesy, geodynamics and celestial mechanics) mainly on the basis of a new high-precision method of angular measurements - radio interferometry with extra-long bases. The technical problems of the new method, the prospects for solving them, ways to achieve extreme measurement accuracy, as well as a number of other problems are discussed in detail. For astrometrists and radio astronomers - specialists, graduate students and students.