In musical instrument classification, string instruments or chordophones, are musical instruments that produce sound from vibrating strings when a performer plays or sounds the strings in some manner.

In organology, the study of musical instruments, many methods of classifying instruments exist. Most methods are specific to a particular cultural group and were developed to serve that culture's musical needs. Culture-based classification methods sometimes break down when applied outside that culture. For example, a classification based on instrument use may fail when applied to another culture that uses the same instrument differently.