Iaido (iaido), also sometimes called iaijutsu (iaijutsu) or battojutsu (battojutsu) is the art of drawing the katana, cutting down the opponent, flipping blood from the blade, and then re-sheathing the katana in one fluid movement. Modern day exponents typically use iaito instead of shinken at least in beginning stages of study.

The emphasis is on drawing the sword and attacking as quickly as possible. Starting positions can be from combative postures or from everyday sitting or standing positions. Practitioners could expect a surprise attack at any time, and the ability to react quickly from an everyday starting position was considered essential.

The Tenshin Shoden Katori Shinto Ryu included iaijutsu in its curriculum in 15th century, and first schools dedicated exclusively to sword drawing appeared some time during the late 16th or early 17th century. Most modern schools consider a samurai called Hayashizaki Jinsuke Minamoto no Shigenobu (1546-1621) as the originator of iaido. Not much is known about his life, and some scholars doubt his existence as a historical figure. The two largest schools of iaido that are practised today, Muso Shinden Ryu and Muso Jikiden Eishin Ryu, both claim a lineage starting with Hayashizaki.

While not a hard and fast rule, frequently the word iaido is used to refer to the modern self improvement oriented form taught by the All Japan Kendo Federation (AJKF) and other iaido associations while iaijutsu is used for the older, combative techniques of the koryu. The word iaido itself was coined by Nakayama Hakudo in early 20th century. Before that various other names like batto, battojutsu, or saya no uchi were used instead.

The most important part of Iai, sometimes called the 'life of iai', is nukitsuke. This is a very quick draw accomplished by drawing the sword out of the saya (scabbard) while drawing the saya itself back. The blade can be brought out of the scabbard and used in a slashing motion very quickly using nukitsuke.