More and more often these days, an instrument originally designed for one purpose or musical genre will be adopted for and adapted to a completely different area. This has been the fate of the resonator guitar, which was originally designed to be louder than a conventional acoustic guitar in order to ensure that the instrument could be heard above the horns and percussion instruments in dance orchestras. The resonator guitar, however, is possessed of a very distinct and original sound, and because of that, it has been adopted and integrated into the musical genres of bluegrass, country and blues music.

The resonator guitar, or resophonic guitar as it is occasionally called, is an acoustic guitar that uses one or more metal cones (resonators) instead of the traditional wooden soundboard. These instruments can be divided into two subcategories, these being square-necked guitars and round-necked guitars. The former are designed to be played like a lap steel guitar (with a slide), while the latter can be played as either a conventional classical guitar or as a steel guitar. In addition to this division, there are also three main types of resonator designs: the "tricone," the single inverted cone, and the spider-less single cone.

The original resonator guitar was developed during the early 20th century and in 1927, the first instruments were manufactured under the brand name National. These guitars were of the tricone variety, which means that they had three conical resonators joined by a T-shaped piece of aluminum called a "spider" that supported the bridge. A year later, one of the founding members of National split and began his own label, Dobro. That company released a competing resonator guitar that featured a single resonator under a distinctive circular perforated metal cover plate. The bridge rested at the center of this plate on an eight-legged aluminum spider. Finally, National countered with its own take on the single resonator model. This instrument used a wooden "biscuit" at the cone apex to support the bridge, rather than the traditional spider.

This quick succession of instrument innovations occurred over the course of about five years. At the end of that time, in 1932, the owners of Dobro gained control of National and formed the National Dobro Corporation. However, with the entry of the United States into World War II in 1941, all production of resonator guitars by the company ceased for a time. Since the end of World War II, the Dobro label has passed through various hands, all of which have used it to produce resonator guitars. Dobro is currently the possession of the Gibson Guitar Company. Today, common terminology uses Dobro to refer to an instrument with an inverted cone, while National generally means an instrument with a non-inverted cone.

As mentioned, bluegrass, country and blues are the usual territory of the resonator guitar. The first generally utilizes square-necked Dobro guitars, while the latter two favor round-necked National instruments. Because both styles of guitar may be played as a lap steel guitar, this is the most common position used by artists. However, round-necked guitars may be played in the traditional guitar position.