This book series is composed of peer-reviewed proceedings of selected symposia organized by the International Association of Geodesy. It deals primarily with topics related to Geodesy Earth Sciences : terrestrial reference frame, Earth gravity field, Geodynamics and Earth rotation, Positioning and engineering applications.

This open access volume contains selected papers of the 2021 Scientific Assembly of the International Association of Geodesy – IAG2021. The Assembly was hosted by the Chinese Society for Geodesy, Photogrammetry and Cartography (CSGPC) in Beijing, China from June 28 to July 2, 2021. It was a hybrid conference with in-person and online attendants. In total, the Assembly was attended by 146 in-person participants and 1,123 online participants. The theme of the Assembly was Geodesy for a Sustainable Earth. 613 contributions (255 oral presentations and 358 poster presentations) covered all topics of the broad spectrum considered by the IAG: geodetic reference frames, Earth gravity field modelling, Earth rotation and geodynamics, positioning and applications, the Global Geodetic Observing System (GGOS), geodesy for climate research, marine geodesy, and novel sensors and quantum technology for geodesy. All published papers were peer-reviewed, and we warmly recognize the contributions and support of the Associate Editors and Reviewers.

This volume gathers the proceedings of the IX Hotine-Marussi Symposium on Mathematical Geodesy, which was held from 18 to 22 June 2018 at the Faculty of Civil and Industrial Engineering, Sapienza University of Rome, Italy. Since 2006, the Hotine-Marussi Symposia series has been produced under the auspices of the Inter-Commission Committee on Theory (ICCT) within the International Association of Geodesy (IAG). The ICCT has organized the last four Hotine-Marussi Symposia, held in Wuhan (2006) and Rome (2009, 2013 and 2018). The overall goal of the ICCT and Hotine-Marussi Symposia has always been to advance geodetic theory, as reflected in the 25 peer-reviewed research articles presented here. The IX Hotine-Marussi Symposium was divided into 10 topical sessions covering all aspects of geodetic theory including reference frames, gravity field modelling, adjustment theory, atmosphere, time series analysis and advanced numerical methods. In total 118 participants attended the Symposium and delivered 82 oral and 37 poster presentations. During a special session at the Accademia Nazionale deiLincei, the oldest scientific academy in the world, six invited speakers discussed interactions of geodesy with oceanography, glaciology, atmospheric research, mathematics, Earth science and seismology.

This open access book contains 30 peer-reviewed papers based on presentations at the 27th General Assembly of the International Union of Geodesy and Geophysics (IUGG). The meeting was held from July 8 to 18, 2019 in Montreal, Canada, with the theme being the celebration of the centennial of the establishment of the IUGG. The centennial was also a good opportunity to look forward to the next century, as reflected in the title of this volume. The papers in this volume represent a cross-section of present activity in geodesy, and highlight the future directions in the field as we begin the second century of the IUGG. During the meeting, the International Association of Geodesy (IAG) organized one Union Symposium, 6 IAG Symposia, 7 Joint Symposia with other associations, and 20 business meetings. In addition, IAG co-sponsored 8 Union Symposia and 15 Joint Symposia. In total, 3952 participants registered, 437 of them with IAG priority. In total, there were 234 symposia and 18 Workshops with 4580 presentations, of which 469 were in IAG-associated symposia.

This open access volume contains the proceedings of the 5th Symposium on Terrestrial Gravimetry: Static and Mobile Measurements (TG-SMM2019) held in St. Petersburg, Russia, October 1 – 4, 2019. The symposium was hosted by the State Research Center of the Russian Federation Concern CSRI Elektropribor, JSC and was attended by 75 participants from 15 different countries. 32 oral and 20 poster contributions were presented in four different topical sessions: Terrestrial, shipboard and airborne gravimetry, Absolute gravimetry, Relative gravimetry, gravity networks and applications of gravimetry and Cold atom and superconducting gravimeters, gravitational experiments.

These proceedings include selected papers from the International Review Workshop on Satellite Altimetry Cal/Val Activities and Applications, held in Chania, Crete, Greece, on 23-26 April 2018. Organised in the context of the European Space Agency Project “Fiducial Reference Measurements for Altimetry” the workshop was cosponsored by the International Association of Geodesy (in particular by the IAG Commission 2, Gravity Field), the European Space Agency, the European Union (the Copernicus Programme), the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), Space Geomatica P.C., and the Municipality of Chania. The workshop presented the latest research in the field of satellite altimetry calibration and altimetry applications for monitoring ocean changes and improving Earth observation in an objective, continuous, homogeneous and reliable manner, free of errors and biases. Further, it supported long-term monitoring of climate change by providing a better understanding of environmental changes in the world's oceans, terrestrial surface waters, and Arctic and Antarctic Regions. The outcome was the creation of a scientific roadmap with procedures, protocols, guidelines, and best practices to help international groups working on satellite altimetry to establish SI (Système International d'Unités) traceability of their measurements, results and data products.