The dreadnought is a type of acoustic guitar body developed by American guitar manufacturer C.F. Martin & Company.^[1] The style, since copied by other guitar manufacturers, has become the most common for acoustic guitars.

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At the time of its creation in 1916 the word dreadnought referred to a large, all big-gun, modern battleship of the type pioneered by HMS Dreadnought in 1906. A body much larger than most other guitars provided the dreadnought with a bolder, perhaps richer, and often louder tone. It is distinguished by its size and square shoulders and bottom. The neck is usually attached to the body at the fourteenth fret.^[1][2]

Martin dreadnought guitars are also known as "D-size" guitars. Their model numbers consist of "D-" followed by a number, such as "D-18" and "D-45".^[3] The higher the numerical designation, the more decorative ornamentation on the instrument.

The dreadnought style was developed in 1916 by Martin specifically for the retailer Oliver Ditson Company. The model was retired after dismal sales. In 1931, after revising the design, Martin began producing dreadnought guitars under its own brand, the first two models named the D-1 and D-2, with bodies made of mahogany and rosewood respectively.^[1]

The popularity of and demand for Martin dreadnought guitars was increased by their use by folk musicians of the mid-20th century, including most bluegrass guitarists. Dreadnoughts became the standard guitar of bluegrass music,^[4] used by many bluegrass musicians to produce a signature sound.

The Gibson Guitar Company's response to the Martin dreadnought was the round-shouldered Jumbo, which it introduced in 1934. It introduced its first square shouldered guitar, the Hummingbird, in 1960.

Since then, dreadnoughts have been made by nearly all major guitar manufacturers worldwide in both standard and single-cutaway forms.

• Chiterra sarda, a traditional large-bodied guitar from Sardinia