Reflecting the broad spectrum of Professor Teunissens research, this Anniversary Volume presents insights into geodetic science, including estimation theory, GNSS observation modelling, Low-Earth-Orbit (LEO) satellites, and InSAR deformation analysis. The book?s chapters serve as informative resources for scientists, engineers, and students in navigation, geodesy, and geospatial engineering. Each chapter is self-contained, allowing standalone reading. Chapter 1 overviews Teunissens work in mathematical geodesy, while Chapter 2 covers subsidence monitoring in the Netherlands since the 1960s. Chapter 3 is devoted to the new terrestrial positioning system of SuperGPS, while Chapters 4?8 discuss advancements in navigation satellite systems. Chapters 9?10 explores the role of emerging LEO satellites in positioning. Inspired by Teunissens contributions to parameter estimation and testing theory, Chapters 11-16 discuss various estimation methods for models with integer and real unknowns. The book concludes with Chapter 17, concerning the important topic of physical geodesy.