Zither (/ˈzɪðər, ˈzɪθ-/; German: [ˈtsɪtɐ], from the Greek word cithara) is 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.