The ocean covers three quarters of the surface of this planet, and is a major factor affecting conditions here. Life originated in the ocean, and continues because of the ocean’s affects on climate. It is also important for transportation, recreation, and resources that include food and pharmaceuticals. Despite this, no one can argue that the ocean is well understood. Measurements are very difficult, and remote sensing will have to play an increasing role in all aspects of ocean science. Important sensors include optical imagers and acoustics on submsersibles and surface ships; LIDAR, radar, multi- and hyper-spectral imagers, and optical and microwave radiometers on aircraft; and optical and microwave imagers and radiometers on satellites. Inferred quantities include ocean surface winds, sea-surface temperature and salinity, sea surface height, ocean color, bathymetry, and distribution and abundance of biota. This special issue attempts to bring together a wide variety of papers on the sensor technology and applications of ocean remote sensing.