The violin is a string instrument with four strings usually tuned in perfect fifths. It is the smallest and highest-pitched member of the violin family of string instruments, which also includes the viola and cello.

The violin is sometimes informally called a fiddle, regardless of the type of music played on it. The word violin comes from the Middle Latin word vitula, meaning stringed instrument; this word is also believed to be the source of the Germanic "fiddle". The violin, while it has ancient origins, acquired most of its modern characteristics in 16th-century Italy, with some further modifications occurring in the 18th century. Violinists and collectors particularly prize the instruments made by the Gasparo da Salò, Giovanni Paolo Maggini, Stradivari, Guarneri and Amati families from the 16th to the 18th century in Brescia and Cremona and by Jacob Stainer in Austria.

A person who makes or repairs violins is called a luthier, or simply a violin maker. The parts of a violin are usually made from different types of wood (although electric violins may not be made of wood at all, since their sound may not be dependent on specific acoustic characteristics of the instrument's construction), and it is generally strung with gut, nylon/steel composite, or steel strings.