Zithers (; German: [ˈtsɪtɐ], from the Greek word cithara) are a class of stringed instruments. Historically, the name has been applied to any instrument of the psaltery family, or to an instrument consisting of many strings stretched across a thin, flat body. This article describes the latter variety.

Zithers are typically played by strumming or plucking the strings with the fingers or a plectrum. In the Hornbostel–Sachs classification system, the term refers to a larger family of similarly shaped instruments that also includes the hammered dulcimer family and piano and a few rare bowed instruments like the bowed psaltery, bowed dulcimer, and streichmelodion. Like an acoustic guitar or lute, a zither's body serves as a resonating chamber (sound box), but, unlike guitars and lutes, a zither lacks a distinctly separate neck assembly. The number of strings varies, from one to more than fifty.

In modern common usage the term "zither" refers to three specific instruments: the concert zither (German: Konzertzither), its variant the Alpine zither (each of which uses a fretted fingerboard), and the chord zither (more recently described as a fretless zither or "guitar zither"). Concert and Alpine zithers are traditionally found in Slovenia, Austria, Hungary, France, north-western Croatia, the southern regions of Germany, Alpine Europe, Poland, the Czech Republic, Slovakia, Russia, Ukraine and Belarus. Emigration from these areas during the 19th century introduced the concert and Alpine zither to North and South America. Chord zithers similar to the instrument in the photograph also became popular in North America during the late 19th and early 20th centuries. These variants all use metal strings, similar to the cittern.