The shamisen or samisen (Japanese: 三味線, literally "three flavor strings"), also called sangen (literally "three strings") is a three-stringed musical instrument played with a plectrum called a bachi. The pronunciation in Japanese is usually "shamisen" (in western Japan, and often in Edo-period sources "samisen") but sometimes "jamisen" when used as a suffix (e.g. Tsugaru-jamisen).

The three strings are traditionally made of silk, or, more recently, nylon. The lowest passes over a small hump at the "nut" end so that it buzzes, creating a characteristic sound known as sawari (somewhat reminiscent of the "buzzing" of a sitar, which is called jawari). The upper part of the dō is almost always protected by a cover known as a dō kake, and players often wear a little band of cloth on their left hand to facilitate sliding up and down the neck. This band is known as a yubikake. There may also be a cover on the head of the instrument, known as a tenjin.
In most genres the shamisen is played with a large weighted plectrum called a bachi, which was traditionally made with ivory or tortoise shell but which now is usually wooden, and which is in the shape likened to a ginkgo leaf. The sound of a shamisen is similar in some respects to that of the American banjo, in that the drum-like skin-covered body, known as a dō, amplifies the sound of the strings. As in the clawhammer style of American banjo playing, the bachi is often used to strike both string and skin, creating a highly percussive sound.
In kouta (小唄; literally "short song") and occasionally in other genres the shamisen is plucked with the fingers.
The shamisen can be played solo or with other shamisen, in ensembles with other Japanese instruments, with singing such as nagauta (長唄), or as an accompaniment to drama, notably kabuki (歌舞伎) and bunraku (文楽). Both men and women traditionally played the shamisen.
The most famous and perhaps most demanding of the narrative styles is gidayū, named after Takemoto Gidayū (1651-1714), who was heavily involved in the bunraku puppet-theater tradition in Osaka. The gidayū shamisen and its plectrum are the largest of the shamisen family, and the singer-narrator is required to speak the roles of the play, as well as to sing all the commentaries on the action. The singer-narrator role is often so vocally taxing that the performers are changed halfway through a scene. There is little notated in the books (maruhon) of the tradition except the words and the names of certain appropriate generic shamisen responses. The shamisen player must know the entire work perfectly in order to respond effectively to the interpretations of the text by the singer-narrator. From the 19th century female performers known as onna-jōruri or onna gidayū also carried on this concert tradition.
In the early part of the 20th century, blind musicians, including Shirakawa Gunpachirō (1909-1962), Takahashi Chikuzan (1910-1998), and sighted ones such as Kida Rinshōei (1911-1979), evolved a new style of playing, based on traditional folk songs ("min'yō") but involving much improvisation and flashy fingerwork. This style - now known as Tsugaru-jamisen, after the home region of this style in the north of Honshū - continues to be relatively popular in Japan. The virtuosic Tsugaru-jamisen style is sometimes compared to bluegrass banjo.
Kouta (小唄) is the style of song learned by geisha and maiko. Its name literally means "small" or "short song," which contrasts with the music genre found in bunraku and kabuki, otherwise known as nagauta (長唄) (long song).
Jiuta (地唄), or literally "earthen music" is a more classical style of shamisen music.
Generally, the thin-necked hosozao is used in nagauta, the shorter and thinner neck facilitating the agile and virtuosic requirements of Kabuki. The hosozao is often used in kouta, where it is plucked with the fingernails. The chuzao is favoured for jiuta, with a broader, more mellow timbre. Finally, the thick-necked futozao is used in the robust music of Gidayubushi (the music of Bunraku), Joruri and Tsugaru-jamisen. In these genres, the thicker neck facilitates the greater force used in playing the music of these styles.
The bachi or plectrums used to play the shamisens also differ in shape. The bachi used for nagauta and jiuta shamisens are very triangular in shape, often having very sharp points. The Gidayu shamisen uses a very slender bachi, having a more subtle triangular shape. The bachi used in tsugaru-jamisen has a noticeable triangular shape, but is still less pronounced than the bachi used in nagauta and jiuta.
The width of the bridge (koma) also varies between genres, and even between schools of playing, such that a jiuta performer of the Ikuta-ryu plays with a different sized koma from that of a Yamada-ryu musician.
Shamisen used for traditional genres of Japanese music, such as jiuta, kouta, and nagauta, adhere to very strict standards. Purists of these genres demand that the shamisens be made of the correct wood, the correct skin, and are played with the correct bachi. There is little room for variation. The tsugaru-jamisen, on the other hand, has lent itself to modern use, and is used in modern genres such as jazz and rock. As a more open instrument, variations of it exist for show. The tuning pegs and bachi, which are usually fashioned out of ivory or turtle shell, for example, are sometimes made of acrylic material to give the shamisen a more modern, flashy look. Recently, avant-garde inventors have developed a Tsugaru-jamisen with electric pickups to be used with amplifiers, like the electric guitar: the electric tsugaru-jamisen has been born.