Fourth Coastal Altimetry Workshop; Porto, Portugal, 14–15 October 2010; Satellite altimetry is now a mature Earth observation technique with great impact in many areas of study, including ocean circulation, marine geoid, bathymetry, and assimilation into models, as well as sea level trends and their impacts on the understanding of global climate change. Until recently, the centimeter-level accuracy achieved by this technique had been limited to open ocean about 50 kilometers off the coast. Aiming to develop products for coastal zones with an accuracy similar to that achieved in the open ocean, several research projects in the past few years, such as Prototype Innovant de Système de Traitement pour les Applications Côtières et l'Hydrologie (PISTACH), Development of Radar Altimetry Data Processing in the Coastal Zone (COASTALT), Centre de Topographie des Océans et de l'Hydrosphère (CTOH), and more recently the European Space Agency Climate Change Initiative (ESA CCI), have been supported by various agencies. In parallel, a set of Coastal Altimetry Workshops was initiated (Silver Spring, Md., 2008; Pisa, Italy, 2008; Frascati, Italy, 2009). The Fourth Coastal Altimetry Workshop followed on this successful series of workshops and was hosted by the University of Porto, with support mainly from ESA and 10 other institutions and space agencies.