Over the past ten years, since the MERIT project began in 1980, great changes have taken place and significant advances made in the area of Earth Rotation and Coordinate Reference Frames. Symposium 105, held at the 125th Anniversary Meeting of the International Association of Geodesy, August 1989, was devoted to this subject. Major improvements in techniques, such as VLBI and laser ranging, have been accompanied by corresponding improvements in data-processing procedures and theories of relevant phenomena. The papers included in this volume provide both a comprehensive record of past discoveries and a sound basis for further advances. Section headings are as follows: - Earth Rotation: Determination and Prediction - Earth Rotation: Interpretation - Reference Frames