A string quintet is a musical piece written for five string musicians. It is based on a string quartet, which includes two violins, one viola, and one cello. A string quintet adds a fifth instrument, often a second viola (called a "viola quintet") or a second cello (called a "cello quintet"). Sometimes, a double bass is used instead.

Examples of famous "viola quintets" with four movements include works by Wolfgang Amadeus Mozart. Other composers, such as Johannes Brahms and Felix Mendelssohn, also wrote "viola quintets." A well-known "cello quintet" is Franz Schubert's Quintet in C major. Antonín Dvořák's Quintet Op. 77 includes a double bass, and Mozart's Eine kleine Nachtmusik can be played with a double bass, though it is not required.

Other instruments sometimes added to a string quartet include a clarinet or piano (such as in a clarinet quintet or piano quintet). A less common type of string quintet uses three violins, one viola, and one cello (a string quartet with an extra violin). Other related musical forms include the string trio and the string sextet.

The term "string quintet" can also describe a group of five musicians who specialize in performing these pieces. This type of ensemble was common in 17th-century Italy and appears as early as 1607 in Claudio Monteverdi's opera, L'Orfeo.

List of viola quintets

• Johann Georg Albrechtsberger – 19 String Quintets called "Sonatas" (1782–1803)
• Franz Joseph Aumann – String Quintet "Divertimento" in C major (around 1760)
• Arnold Bax – Quintet (1933)
• Frank Bridge – Quintet in E minor (H15, 1901)
• Ludwig van Beethoven – Quintet, Op. 29, sometimes called the Storm Quintet; a Fugue in D major for viola quintet, Op. 137; an arrangement of his Octet for Viola Quintet, Op. 4 (the original Octet was later published as Op. 103); an arrangement of his Piano Trio Op. 1 No. 3 for Viola Quintet, Op. 104
• Luigi Boccherini – twelve original quintets and arrangements of his twelve piano quintets (Op. 56 and Op. 57) for viola quintet
• Johannes Brahms – two quintets, Op. 88 and Op. 111; the first edition of the Clarinet Quintet Op. 115 included an alternate part for viola instead of the clarinet
• Max Bruch – Quintet in A minor
• Anton Bruckner – String Quintet in F major (1879); Intermezzo in D minor (used instead of the scherzo)
• Carson Cooman – Quintet (Unquiet Parables, 2009), Op. 856
• Brett Dean – Epitaph for string quintet (2010)
• Antonín Dvořák – two quintets, No. 1 in A minor and No. 3 in E flat (the American Quintet)
• Victor Ewald – Quintet Op. 4 in A major
• Eduard Franck – two quintets, Op. 15 in E minor and Op. 51 in C major
• Florian Leopold Gassmann – Op. 2 six String Quintets H 501–506 (1772)
• Friedrich Gernsheim – Quintet Op. 9 in D
• Roy Harris – Quintet (1940)
• Franz Joseph Haydn – Hob.II:2 Divertimento in G major (around 1754)
• Heinrich von Herzogenberg – Quintet in C minor, Op. 77 (1892)
• Franz Anton Hoffmeister – Op. 2 six quintets (around 1782)
• Klaus Huber – Ecce homines (1998)
• Heinrich Kaminski – Quintet in F sharp minor (two versions, first 1916)
• Franz Krommer – fifteen String Quintets
• Johann Michael Malzat – six String Quintets in F, G, B, A, E flat, and C major
• Bohuslav Martinů – Quintet (1927)
• Felix Mendelssohn – two quintets: No. 1 in A major, Op. 18 (1826, revised 1832) and No. 2 in B flat major, Op. 87 (1845)
• Ernst Mielck – Quintet in F major (1897)
• Darius Milhaud – Quintet Op. 325 (1953–1954)
• Wolfgang Amadeus Mozart – six quintets: K174, K406/516b, K515, K516, K593, K614
• Carl Nielsen – Quintet in G major (1888)
• George Onslow – five of his thirty-four quintets include two violas; four include a double bass, and the rest include two cellos
• Hubert Parry – Quintet in E flat (1909)
• George Perle – Quintet (1958)
• Josef Rheinberger – Quintet in A minor, Op. 82 (1874)
• Ferdinand Ries – Seven Quintets, Op. 37 in C, Op. 68 in D minor, Op. 167 in A minor, Op. 171 in G, Op. 183 in E flat, and two published without opus in A major and F minor (published in a series "Samtliche Streichquintette" edited by Jürgen Schmidt between 2003–2005 for Accolade Musikverlag)
• Franz Schubert – "Quintet-Overture" for Quintet, D 8
• Roger Sessions – Quintet (1958)
• Robert Simpson – Quintet (1987)
• Louis Spohr – seven Quintets
• Charles Villiers Stanford – Two Quintets, Op. 85 and Op. 86
• Johan Svendsen – Quintet in C, Op. 5 (1868)
• Sergei Taneyev – Quintet in C, Op. 16
• Johann Baptist Wanhal – Six String Quintets (1774)
• Ralph Vaughan Williams – Quintet (the Phantasy Quintet – 1912) and Nocturne and Scherzo (1904–1906)
• Felix Weingartner – Quintet, his Op. 40
• Ermanno Wolf-Ferrari – Quintet in C, Op. 24 (1939)
• John Woolrich – The Death of King Renaud (1991)
• Alexander von Zemlinsky – Quintet (1894–1896): 2 movements are lost

List of cello quintets

• Arnold Bax – Quintet in G major (1908), the second movement of which was rewritten for a Viola Quintet and published as the Lyrical Interlude (1923);
• Wilhelm Berger – Quintet in E minor, Op. 75 (1911)
• Luigi Boccherini – one hundred and ten Quintets. The third movement Minuet from the Cello Quintet Op.11 No.5 is very famous.
• Alexander Borodin – Quintet in F minor (1859–1860)
• Luigi Cherubini – Quintet in E minor (1837)
• Felix Otto Dessoff – Quintet, Op. 10
• Friedrich Dotzauer – Quintet in D minor, Op. 134 (1835)
• Felix Draeseke – Quintet in F, Op. 77 (1901)
• Friedrich Gernsheim – Quintet Op. 89 in E♭
• Alexander Glazunov – Quintet in A, Op. 39 (1892)
• Karl Goldmark – Quintet in A minor, Op. 9 (1862)
• Theodore Gouvy – Quintet in G, op. 55 is on IMSLP
• August Klughardt – Quintet in G minor, Op. 62 (1902)
• Frank Martin – Pavane "Colour of Weather" (1920, 7 minutes, for quintet)
• Darius Milhaud – Quintet Op. 350 (1956)
• George Onslow – twenty-five of his thirty-four string quintets are Cello Quintets; five include two violas, and four feature a double bass
• Einojuhani Rautavaara – Quintet "Les Cieux Inconnues" (Unknown Heavens, 1997)
• Ottorino Respighi – Quintet in G minor (1901, incomplete)
• Wolfgang Rihm – Epilog (2013)
• George Rochberg – Quintet for Two Violins, Viola and Two Cellos (1982)
• Franz Schubert – Cello Quintet, Op. post. 163, D 956
• Peter Seabourne – Quintet for Two Violins, Viola and Two Cellos (2012)
• Robert Simpson – Quintet (1995)
• Ethel Smyth – Quintet in E major, Op. 1
• Sergei Taneyev – Quintet in G, Op. 14 (1900–1901)
• Ferdinand Thieriot – String Quintet in G major, 1914; others with wind instruments
• Carl Vine – String Quintet (2009)

String quintets for 3 violins, viola and cello

• Johann Georg Albrechtsberger, String Quintet composed in 1798
• Franz Clement, Introduction and Polonaise in E major (Polonaise for Violin with Accompaniment of Two Violins, Viola, and Cello)
• Heinrich Wilhelm Ernst, Polonaise, Opus 17
• Morton Feldman, Violin and String Quartet composed in 1985
• Charles Martin Loeffler, a Violin Quintet (comprising three violins, a viola, and a cello)
• Joseph Mayseder, Polonaise No. 1, Opus 10; Polonaise No. 3, Opus 12
• Alessandro Rolla, Divertimento for Violin and String Quartet, BI 429
• Franz Schubert, Rondo in A major for Violin and Strings, D 438
• Louis Spohr, Potpourri No. 2 in B-flat major (Potpourri on Themes by Mozart for Violin and String Quartet (with bass ad libitum))

List of double bass quintets

• Leslie Bassett – Quintet (1957)
• Luigi Boccherini – three Quintets.
• Antonín Dvořák – Quintet Opus 77 in G (1875)
• Brian Ferneyhough – Christus Resurgens (2017)
• Alistair Hinton – String Quintet (1969–1977)
• Vagn Holmboe – Quintet, Opus 165/M.326 (1986)
• Darius Milhaud – Quintet Opus 316
• Wolfgang Amadeus Mozart – Serenade No. 13, K. 525, "Eine kleine Nachtmusik"
• George Onslow – Four of his thirty-four String Quintets include a double bass. Five have two violas, and the remaining ones have two cellos.
• Robert Paterson – I See You (2015) (for string quintet with double bass and a recording)

String quintets for other combinations

Felix Draeseke composed a five-part musical piece titled "Quintet in A" for two violins, a viola, a violotta, and a cello, known as the Stelzner-Quintett (1897). He also wrote a cello quintet in F, Op. 77 (1901).