太空衣是保护宇航员在太空不受低温，射线等的侵害并提供人类生存所需的氧气的保护服。

太空衣的：氧气罐为太空人提供氧气。而排出的二氧化碳则由氢氧化锂（lithium hydroxide）所吸收。太空衣的表层有阻隔辐射的功用。太空人的体温则由一套贴身内衣调节，这件内衣布满水管，水泵不断把水循环，把太空人身体所发出的热力带走，而水则由升华器（sublimator）所冷却。太空衣最后一个重要功用，是为太空人提供所需的气压（约等于半个标准大气压力52kpa）；如果气压过低，人体血液及身体组织内的气体会离开，令太空人患上类似潜水员常有的潜水病（在真空的情况下，太空人更会由于血液瞬间「沸腾」而死亡）。

A space suit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, and are necessary for extravehicular activity (EVA), work done outside spacecraft. Space suits have been worn for such work in Earth orbit, on the surface of the Moon, and en route back to Earth from the Moon. Modern space suits augment the basic pressure garment with a complex system of equipment and environmental systems designed to keep the wearer comfortable, and to minimize the effort required to bend the limbs, resisting a soft pressure garment's natural tendency to stiffen against the vacuum. A self-contained oxygen supply and environmental control system is frequently employed to allow complete freedom of movement, independent of the spacecraft.