A catalog containing milliarcsecond-accurate positions of 1332 extragalactic radio sources distributed over the northern sky is presented—the Very Long Baseline Array Calibrator Survey (VCS1). The positions have been derived from astrometric analysis of dual-frequency 2.3 and 8.4 GHz VLBA snapshot observations; in a majority of cases, images of the sources are also available. These radio sources are suitable for use in geodetic and astrometric experiments, and as phase-reference calibrators in high-sensitivity astronomical imaging. The VCS1 is the largest high-resolution radio survey ever undertaken and triples the number of sources available to the radio astronomy community for VLBI applications. In addition to the astrometric role, this survey can be used in active galactic nuclei, Galactic, gravitational lens, and cosmological studies.

VLBI has been used for high precision EOP measurements since 1980. The typical formal error for current routine monitoring of polar motion is similar to 80 mu as. A program for continuous EOP observations using VLBI is being incrementally implemented. There are unexplained differences between EOP values derived from simultaneously observing networks.