Carrageenans are natural polymers, obtained by water extraction from the algae of the Rhodophytae class. Chemically they are K-, Na-, Mg- and Ca- salts of the polysaccharides sulfated esters. There are three carrageenans types depending on sulfat contents (κ, ι ,λ). This paper presents the structures, the physicochemical properties, the methods and the possible uses of these polymers. Their characteristics and properties recommends their use as excipients for pharmaceutical technology.