**1. Introduction**

Radar satellite altimetry provides global, frequent, and precise measurements of uniform accuracy of the sea level height related to a desired geodetic reference frame at different time epochs and from various altimeter sensors. Designed in 1969 at the Williamstown Conference on Solid Earth and Ocean Physics [1, 2], the technology was developed through the experimental missions Skylab (see [3]), Geodynamics Experimental Ocean Satellite 3 (GEOS-3, see [4]), and SEAfaring SATellite (SEASAT, see [5]). Since the early 1990s, different altimeter satellite missions provide reliable and solid information on the sea level thus enabling various applications in geodesy, oceanography, glaciology, climate research, atmosphere, wind, waves, biology, and navigation [6, 7]. To this day, more than 80,000 publications discuss or include altimeter data, technology, or products [8].

In geodesy, satellite altimetry is used to study Earth's shape and size, sea-level variability, Earth's gravity field over oceans and its change, tectonic plate motion, bathymetry, natural hazards, and inland water-related occurrences. The data acquired by the satellite altimeters are distributed at different levels of complexity and applicability; from source, non-processed measurements, which must be

corrected using various atmospheric and geophysical models and corrections, up to complete products ready to use in different applications. The measurements are distributed with different timeliness, most often in near real-time (e.g., in less than 3 hours after the acquisition).

This book chapter presents the theoretical background of the technology, basic principles and data processing procedures, current trends in technology, and different applications of the technology. The chapter gives an overview of the relevant literature and points towards more specific studies.
