The hammered dulcimer (also known as the hammer dulcimer) is a stringed musical instrument with the strings stretched over a trapezoidal sounding board. The instrument is typically set at an angle on a stand in front of the musician, who holds a small mallet, called a hammer in each hand with which to strike the strings (for the plucked Appalachian dulcimer, see Appalachian dulcimer). The word dulcimer comes from the Latin dulcis or "sweet" and the Greek melos, meaning "song". The origin of the instrument is uncertain, but tradition holds that it was invented in Iran roughly 2000 years ago, where it is called a Santur.

The instrument has seen somewhat of a revival in America in the American folk music traditions. It is also still played in Wales, East Anglia, Northumbria, the Middle East, the People's Republic of China and Thailand. It is also used in traditional folk music in Austria and Bavaria.

The hammered dulcimer comes in various sizes, identified by the number of strings that cross each of the bridges. A 15/14, for example, has two bridges (treble and bass) and spans three octaves. The strings of a hammered dulcimer are usually found in pairs, two strings for each note (though some instruments have three or four strings per note). Each set of strings is tuned in unison and is called a course. As with a piano, the purpose of using multiple strings per course is to make the instrument louder, although as the courses are rarely in perfect unison, a chorus effect usually results. A hammered dulcimer, like an autoharp or harp, requires a tuning wrench for tuning. Unlike the strings of a guitar, the dulcimer's strings are wound around simple bolts (called tuning pins) with square heads.

The strings of the hammered dulcimer are often tuned diatonically, according to a circle of fifths pattern. Typically, the lowest note (often a G or D) is found on the lower right-hand corner of the instrument, just to the left of the right-hand (bass) bridge. As a player strikes the courses above in sequence, they ascend the diatonic scale based on the G or D. With this tuning, the scale is broken into two tetrachords, or groups of four notes. For example, on an instrument with D as the lowest note, the D major scale is played starting in the lower-right corner and ascending the bass bridge: D - E - F# - G. This is the lower tetrachord of the D major scale. At this point the player returns to the bottom of the instrument and shifts to the treble bridge to play the higher tetrachord: A - B - C# - D.

This shift to the adjacent bridge is required because the bass bridge's fourth string G is the start of the lower tetrachord of the G scale. If the player ascends the first eight strings of the bass bridge, they will encounter a flatted seventh (C natural in this case), because this note is drawn from the G tetrachord. This D major scale with a flatted seventh is the mixolydian mode in D.

The pattern continues to the top of the instrument and to the left-hand side of the treble bridge. Moving from the left side of the bass bridge to the right side of the treble bridge is analogous to moving from the right side of the treble bridge to the left side of the treble bridge.

This diatonically-based tuning results in most, but not all, notes of the chromatic scale being available in each key. To fill in the gaps, many modern dulcimer builders include extra short bridges at the top and bottom of the soundboard, where extra strings are tuned to some or all of the missing pitches. Such instruments are often called "chromatic dulcimers" as opposed to the more traditional "diatonic dulcimers".

Hammered dulcimers of non-European descent may have other tuning patterns, and builders of European-style dulcimers sometimes experiment with alternate tuning patterns.

The hammered dulcimer derives its name from the small mallets that players use to strike the strings, called hammers. They are usually made of wood, but can be made from any material, including metal and plastic. In the Western hemisphere, hammers are usually stiff, but in Asia, flexible hammers are often used. The head of the hammer can be left bare for a sharp attack sound, or can be covered with adhesive tape, leather, or fabric for a softer sound.

Several traditional players have used hammers that differ substantially from those in common use today. Paul Van Arsdale (b. 1920), a player from upstate New York, uses flexible hammers made from hacksaw blades, with leather-covered wooden blocks attached to the ends (these are modeled after the hammers used by his grandfather, Jesse Martin). The Irish player John Rea (1915-1983) used hammers made of thick steel wire, wound with wool. Billy Bennington (1900-1986), a player from Norfolk county in England, used cane hammers bound with wool.

The hammered dulcimer (as well as the mountain dulcimer), can also be bowed, though this is not a widespread practice, as a traditional bow would do little good. In order to make bowing the instrument possible, bowhammers, and more recently Jimbows, were created. Bowhammers are a unique invention used by musician Michael Masley. Jimbows consist of a wooden handle connected to a curved nylon rod, which when rosined, will produce the desired sound.

Versions of the hammered dulcimer are used throughout the world. In Eastern Europe a larger descendant of the hammered dulcimer called the cimbalom is played and has been used by a number of classical composers, including Zoltán Kodály and Igor Stravinsky, and more recently by Blue Man Group. The khim is a Thai hammered dulcimer. The Chinese yangqin is a type of hammered dulcimer that originated in Persia. The Santur and Santoor are found in the Middle East and India, respectively.

• Austria - Hackbrett
• Belarus - Цымбалы (Tsymbaly)
• Brazil - saltério
• Cambodia - khim
• China - yangqin
• Czech Republic - cimbál
• Denmark - hakkebræt
• France - Tympanon
• Germany - Hackbrett
• Greece - santouri
• Hungary - cimbalom
• India - santoor
• Iran - santur
• Ireland - tiompan
• Italy - salterio
• Korea - yanggeum
• Laos - khim
• Lithuania - cimbalai, cimbolai
• Mexico - salterio
• Mongolia joochin
• Netherlands - hakkebord
• Romania - ţambal
• Russia - Цимбалы (Tsymbaly), Дульцимер (Dultsimer)
• Spain - salterio
• Sweden - hackbräda, hammarharpa
• Switzerland - Hackbrett
• Thailand - khim
• Turkey - santur
• Ukraine - Цимбали (Tsymbaly)
• United Kingdom - hammered dulcimer
• United States - hammered dulcimer
• Vietnam - Đàn tam thập lục (lit. "36 strings")
• Yiddish - tsimbl