双体船（英语：catamaran，简称：cat，源自泰米尔文）是把2个瘦长以上的船体横向连在一起组成的连体船，船体间用甲板桥连接，各具独立的推动设备。〈若把3个船体一起串联，则称为三体船 (英语：trimaran) 〉由于2艘小船横向连接在一起，在海上可承受较大的风浪，不易翻船。在高速时，两个较瘦长的船体可以大幅降低船身的阻力。而且同吨位下总宽度较大，具有较高的运输效率，常见于竞技及娱乐用的船只设计。

双体船虽然在燃料推动船只的范畴中是一种相对较新的设计，但其实在太平洋上的波利尼西亚，双体船的使用已经历了数个世纪。在中国更使用了超过二千年。

A catamaran (/ˌkætəməˈræn/) (informally, a "cat") is a multi-hulled watercraft featuring two parallel hulls of equal size. It is a geometry-stabilized craft, deriving its stability from its wide beam, rather than from a ballasted keel as with a monohull sailboat. Being ballast-free and therefore lighter than a monohull, catamarans often have a shallower draft (draught) than comparably-sized monohulls. The two hulls combined also often have a smaller hydrodynamic resistance than comparable monohulls, requiring less propulsive power from either sails or motors. The catamaran's wider stance on the water can reduce both heeling and wave-induced motion, as compared with a monohull.