Aiki-ken (Kanji: 合気剣 Hiragana: あいきけん) is the name given specifically to the set of Japanese sword techniques practiced according to the principles of aikido, taught first by Morihei Ueshiba (aikido's founder), then further developed by Morihiro Saito, one of Ueshiba's most prominent students. Currently, Iwama Shin-Shin Aiki Shuren-kai is the main proponent organization.
Much of the aiki-ken syllabus was developed by Morihei Ueshiba (植芝 盛平 Ueshiba Morihei, 1883–1969) at his dojo in Iwama, Japan, at the same time he developed aikido's staff training (called aiki-jō). It is well documented that Ueshiba studied several different styles of kenjutsu (Japanese swordsmanship), but the aiki-ken techniques are predominantly based upon the teachings of the Kashima Shintō-ryu.
The practice of aiki-ken is not pervasive. Some schools of aikido incorporate weapons training that is unrelated to aiki-ken, and others forego weapons training entirely.
Much of aiki-ken bears little similarity to other modern sword arts. Rather than learning to "fight" with swords, the primary purpose of aiki-ken is to magnify errors in one's aikido technique, and to give the student an opportunity to apply the principles of aikido in different situations. Aiki-ken is practiced using bokken (a wooden katana) and has a wide variety of techniques. Saito codified two sets of techniques, the first being seven suburi (solo cutting exercises), and the second being five partnered forms. Some dojo also practice jiyu-waza armed with bokken (freestyle technique, without a predetermined form of attack and response).
Suburi (素振り:すぶり?), a word that translates literally to something like "elementary swinging", is used to refer to the basic solo movements of aiki-ken, developed as a distillation of the partnered practice.