A zither is a stringed musical instrument that is played by strumming or plucking the strings with the fingers or a pick. The body of a zither serves as a resonating chamber, but unlike guitars and lutes, a zither lacks a distinctly separate neck assembly. The number of strings on a zither varies, from one to more than fifty. The word "zither" is derived from the Latin word "cythara," which was used for the title covers on many 16th and 17th century German printed manuscript books originally for the "cittern" – from the Greek word "kithara," an instrument used in Ancient Greece.

There are many types of zithers, but in modern common usage, the term "zither" refers to three specific instruments: the concert zither, its variant the Alpine zither, and the chord zither. The concert and Alpine zithers are traditionally found in Slovenia, Austria, Hungary, France, north-western Croatia, the southern regions of Germany, and alpine Europe. The chord zither is more recently described as a fretless zither or "guitar zither".

The European zither consists of a flat, shallow soundbox across which some 30 or 40 gut or metal strings are stretched. With some zithers, the melody strings are stopped by pressing them against the frets with a short metal bar, a way of playing preserved on the American variety, the Appalachian, or mountain, dulcimer. There are also zithers that are bowed rather than plucked, such as the Korean ajaeng.

Zithers are often used in European folk music and have been used in England since the mid-1850s. The zither orchestra, which started up a hundred years ago, comes from Ludwigsburg, Germany.