A luthier ( LOO-ti-ər; AmE also LOO-thi-ər) is a craftsperson who builds or repairs string instruments that have a neck and a sound box. The word "luthier" is originally French and comes from the French word for lute. The term was originally used for makers of lutes, but it came to be used already in French for makers of most bowed and plucked stringed instruments such as members of the violin family (including violas, cellos, and double basses) and guitars. Luthiers, however, do not make harps or pianos; these require different skills and construction methods because their strings are secured to a frame.

The craft of luthiers, lutherie (rarely called "luthiery", but this often refers to stringed instruments other than those in the violin family), is commonly divided into the two main categories of makers of stringed instruments that are plucked or strummed and makers of stringed instruments that are bowed. Since bowed instruments require a bow, the second category includes a subtype known as a bow maker or archetier. Luthiers may also teach string-instrument making, either through apprenticeship or formal classroom instruction.