软骨鱼类是一种古老的鱼类，进化自盾皮鱼。

软骨鱼和硬骨鱼，一起出现在泥盆纪，它们不断进化，最后取代了盾皮鱼类。现存的2万多种鱼类中，根据其骨骼的性质，可分为软骨鱼和硬骨鱼两大类。

软骨鱼类是鱼类中最低等的类群，骨骼全部由软骨组成，体被盾鳞或无鳞；鳃裂每侧5－7个分别开口于体外，或4个外被一膜质鳃盖；雄性的腹鳍里侧具有鳍脚；尾鳍呈歪尾型；肠具有螺旋瓣；无鳔；软骨鱼类的生殖方式是体内受精，卵生、卵胎生或胎生。

绝大多数在海洋中生活，但它们却起源于淡水生活的祖先。

现存的软骨鱼类主要分为两个亚纲：

Chondrichthyes (/kɒnˈdrɪkθᵻ.iːz/; from Greek χονδρ- chondr- 'cartilage', ἰχθύς ichthys 'fish') is a class that contains the cartilaginous fishes: they are jawed vertebrates with paired fins, paired nares, scales, a heart with its chambers in series, and skeletons made of cartilage rather than bone. The class is divided into two subclasses: Elasmobranchii (sharks, rays, skates, and sawfish) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class).