Iai is considered a classical bujutsu or budo. It is more difficult to characterize iai, as the student progresses the -do aspects are left behind and the -jutsu aspects become more pronounced. Iai is believed to have its origins about 1200 AD, with about 800 ryu cataloged since then. It is possible that the present art of iai had its origins in an ancient reference to "tachi-gake" from about 1000 AD.
Iai is differentiated from the ken styles in that the sword is initailly at rest in the scabbard instead of already drawn for combat. Iai is composed of drawing the sword (nukitsuke), bringing it to combative use in minimum time, and returning the sword to the saya (scabbard). Starting positions for iai can be from combative postures or from everyday setting or standing positions.
Traditional gi are worn as in kenjutsu. Advancement can be either in the traditional method, without dan and kyu, or can include it similar to kendo. Iai within the Zen Nihon Kendo Renmei is ranked, and several instructor credentials are also available; called renshi, kyoshi and hanshi, which are also available in kendo.
The reason for the kendo federation having oversight of iaido is quite simple. Early this century, kendo practioners were aware that kendo was not properly teaching the sword. A shinai is not a Nihon-to (Japanese sword) and does not handle like a sword. Kendo did retain ten kata as a part of their promotion process, but they were felt to be insufficient to properly teach the "way of the sword."
In the late 1950s the Kendo Federeation invited classical iai expert swordsmen to form a commission to investigate courses of action. The result was a selection and adoption of seven iai kata. This list was later revised to ten kata by a later comission. These kata formed the basis of the Zen Nihon Kendo Renmei Seitei Gata.
These ten kata form the basis of kendo based iai. Further advancement is made within classical ryu. Examples are the Muso Jikiden Eishin Ryu and the Muso Shinden Ryu. These two ryu are splits of the same branch and remain quite probably the most practiced ryu of iaido. These were the first to allow the public to join their ranks and participate as outsiders.
The Seitei Gata have three opening positions. Seiza is used for the first three and is considered a non-combative position. Tate-hiza is used for the fourth kata and is considered neutral, that is neither combative or non-combative. Finally, the last six kata are started from tachi-ai, and is also considered neutral. There is one other opening position which is considered combative but is not used in seitei, called iai-goshi.
The reason for non-combative or neutral starts is that these are the positions of everyday life. One could expect a surprise attack at anytime, and the ability to react from an everyday starting position was considered essential.
A complete list of the Seitei and the the Muso Shinden Ryu kata are included below.