Within the national German geoscientific research and development programme "GEOTECHNOLOGIEN," funded by the Federal Ministry of Education and Research (BMBF) and the German Research Foundation (DFG), the research theme "Observation of the System Earth from Space" was selected as one of 13 key areas in this programme. During the first research phase for this theme from 2002 to 2004 six projects were accomplished covering Earth gravity field and Earth rotation research. These six projects are related to the data exploitation and preparation of analysis techniques for the gravity field satellite missions CHAMP, GRACE and GOCE, to the integration of geodetic observation techniques for a user centre within the International Earth Rotation Service and to improvements in observation and analysis techniques for airborne gravimetry and ring lasers. This book provides a detailed summary of the obtained results, which are relevant for a broad scientific community working in gravity field and Earth rotation research.