Japanese sword mountings are the various housings and associated fittings (tosogu) that hold the blade of a Japanese sword when it is being worn or stored. Koshirae (拵え) refers to the ornate mountings of a Japanese sword (e.g. katana) used when the sword blade is being worn by its owner, whereas the shirasaya is a plain undecorated wooden mounting composed of a saya and tsuka that the sword blade is stored in when not being used.

A shirasaya (白鞘), "white scabbard", is a plain wooden Japanese sword saya (scabbard) and tsuka (hilt), traditionally made of honoki (bigleaf magnolia) wood and used when a blade was not expected to see use for some time and needed to be stored. They were externally featureless save for the needed mekugi-ana to secure the nakago (tang), though sometimes sayagaki (blade information) was also present. The need for specialized storage is because prolonged koshirae mounting harmed the blade, owing to factors such as the lacquered wood retaining moisture and encouraging corrosion.

Such mountings are not intended for actual combat, as the lack of a tsuba (guard) and proper handle wrappings were deleterious; as such they would likely never make their way onto a battlefield. However, there have been loosely similar "hidden" mountings, such as the shikomizue. Also, many blades dating back to earlier Japanese history are today sold in such a format, along with modern-day reproductions; while most are purely decorative replicas, a few have functional blades.

The word koshirae is derived from the verb koshiraeru (拵える), which is no longer used in current speech. More commonly "tsukuru" is used in its place with both words meaning to "make, create, manufacture." A more accurate word is tōsō (刀装), meaning sword-furniture, where tōsōgu (刀装具) are the parts of the mounting in general, and "kanagu" stands for those made of metal. Gaisō (外装) are the "outer" mountings, as opposed to tōshin (刀身), the "body" of the sword.

A koshirae should be presented with the tsuka (hilt) to the left, particularly in times of peace with the reason being that one cannot unsheathe the sword easily this way. During the Edo period, many formalized rules were put into place: in times of war the hilt should be presented to the right allowing the sword to be readily unsheathed.

Koshirae were meant not only for functional but also for aesthetic purposes, often using a family mon (crest) for identification.

The tachi (太刀) style koshirae is the primary style of mounting used for the tachi, where the sword is suspended edge-down from two hangers (ashi) attached to the obi. The hilt often had a slightly stronger curvature than the blade, continuing the classic tachi increase in curvature going from the tip to the hilt. The hilt was usually secured with two pegs (mekugi), as compared to one peg for shorter blades including katana. The tachi style koshirae preceded the katana style koshirae.

The katana (刀) style koshirae is the most commonly known koshirae and it is what is most associated with a samurai sword. Swords mounted in this manner are worn with the cutting edge up as opposed to the tachi mounting, in which the sword is worn with the cutting edge down.