The National String Instrument Corporation was an American guitar company first formed to manufacture banjos and then the original resonator guitars. National also produced resonator ukuleles and resonator mandolins. The company merged with Dobro to form the "National Dobro Company", then becoming a brand of Valco until it closed in 1968.

A resonator guitar or resophonic guitar is an acoustic guitar that produces sound by conducting string vibrations through the bridge to one or more spun metal cones (resonators), instead of to the guitar's sounding board (top). Resonator guitars were originally designed to be louder than regular acoustic guitars, which were overwhelmed by horns and percussion instruments in dance orchestras. They became prized for their distinctive tone, and found life with bluegrass music and the blues well after electric amplification solved the problem of inadequate volume.