Kenneth Seidelmann is a Research Professor in the Department of Astronomy, University of Virginia. Until 2000, was Director of Astrometry of the U.S. Naval Observatory, and a Visiting Professor at the University of Maryland. Jean Kovalevsky is an Associate (retired) Astronomer of the Centre de Recherches et d'Etudes Geodynamiques et Astronomiques (CERGA), at the Observatoire de la Cote d'Azur, France. He is President of the International Committee of Weights and Measures and a member of the French Academy of Sciences.

• 1. Introduction; 2. New observational techniques; 3. Basic principles and coordinate systems; 4. Treatment of astronomical data; 5. Principles of relativity; 6. Apparent displacements of celestial objects; 7. Extragalactic reference frame; 8. Dynamical reference frame; 9. Terrestrial coordinate systems; 10. Earth orientation; 11. Stars; 12. Double and multiple star systems; 13. Astronomical phenomena; 14. Application of theory to observations; Appendices.

Kenneth Seidelmann is a Research Professor in the Department of Astronomy, University of Virginia. Until 2000, was Director of Astrometry of the U.S. Naval Observatory, and a Visiting Professor at the University of Maryland. Jean Kovalevsky is an Associate (retired) Astronomer of the Centre de Recherches et d'Etudes Geodynamiques et Astronomiques (CERGA), at the Observatoire de la Cote d'Azur, France. He is President of the International Committee of Weights and Measures and a member of the French Academy of Sciences.

• 1. Introduction; 2. New observational techniques; 3. Basic principles and coordinate systems; 4. Treatment of astronomical data; 5. Principles of relativity; 6. Apparent displacements of celestial objects; 7. Extragalactic reference frame; 8. Dynamical reference frame; 9. Terrestrial coordinate systems; 10. Earth orientation; 11. Stars; 12. Double and multiple star systems; 13. Astronomical phenomena; 14. Application of theory to observations; Appendices.

Kenneth Seidelmann is a Research Professor in the Department of Astronomy, University of Virginia. Until 2000, was Director of Astrometry of the U.S. Naval Observatory, and a Visiting Professor at the University of Maryland. Jean Kovalevsky is an Associate (retired) Astronomer of the Centre de Recherches et d'Etudes Geodynamiques et Astronomiques (CERGA), at the Observatoire de la Cote d'Azur, France. He is President of the International Committee of Weights and Measures and a member of the French Academy of Sciences.

• 1. Introduction; 2. New observational techniques; 3. Basic principles and coordinate systems; 4. Treatment of astronomical data; 5. Principles of relativity; 6. Apparent displacements of celestial objects; 7. Extragalactic reference frame; 8. Dynamical reference frame; 9. Terrestrial coordinate systems; 10. Earth orientation; 11. Stars; 12. Double and multiple star systems; 13. Astronomical phenomena; 14. Application of theory to observations; Appendices.