An Acoustic guitar is not dependent on any external device for amplification. The shape and resonance of the guitar itself creates acoustic amplification. However, the unamplified guitar is not a loud instrument. It cannot compete with other instruments commonly found in bands and orchestras, in terms of sheer audible volume. Many acoustic guitars are available today with built-in electronics and power to enable amplification.

There are several subcategories within the acoustic guitar group: steel string guitars, which includes the flat top, or "folk" guitar, the closely related twelve string guitar, and the arch top guitar. A recent arrival in the acoustic guitar group is the acoustic bass guitar, similar in tuning to the electric bass.

Renaissance and Baroque guitars: These are the gracile ancestors of the modern classical guitar. They are substantially smaller and more delicate than the classical guitar, and generate a much quieter sound. The strings are paired in courses as in a modern 12 string guitar, but they only have four or five courses of strings rather than six. They were more often used as rhythm instruments in ensembles than as solo instruments, and can often be seen in that role in early music performances. (Gaspar Sanz' Instrucción de Música sobre la Guitarra Española of 1674 constitutes the majority of the surviving solo corpus for the era.) Renaissance and Baroque guitars are easily distinguished because the Renaissance guitar is very plain and the Baroque guitar is very ornate, with inlays all over the neck and body, and a paper-cutout inverted "wedding cake" inside the hole. See article: Baroque guitar.

Classical guitars: These are typically strung with nylon strings, played in a seated position and are used to play a diversity of musical styles including classical music. The classical guitar is designed to allow for the execution of solo polyphonic arrangements of music in much the same manner as the pianoforte can. This is the major point of difference in design intent between the classical instrument and other designs of guitar. Flamenco guitars are very similar in construction, have a sharper sound, and are used in flamenco. In Mexico, the popular mariachi band includes a range of guitars, from the tiny requinto to the guitarron, a guitar larger than a cello, which is tuned in the bass register. In Colombia, the traditional quartet includes a range of instruments too, from the small bandola (sometimes known as the Deleuze-Guattari, for use when travelling or in confined rooms or spaces), to the slightly larger tiple, to the full sized classical guitar. Modern dimensions of the classical instrument were established by Antonio Torres Jurado (1817-1892). Classical guitars are sometimes referred to as classic guitars, which is a more proper translation from the Spanish.

Portuguese guitar: Is a 12 string guitar used in Portugal for the traditional Fado song. Its true origins are somewhat uncertain but there is a general agreement that it goes back to the medieval period. It is often mistakenly thought of to be based on the so-called "English guitar" - a common error as there is no such thing. For some time the best instruments of this and other types were made in England, hence the confusion. "English guitar" refers to a quality standard, not really an instrument type. This particular instrument is most likely a merge of medieval "cistre" or "citar" and the arabic lute.

Flat-top (steel-string) guitars: Similar to the classical guitar, however the body size is usually significantly larger than a classical guitar and it has a narrower, reinforced neck and stronger structural design, to sustain the extra tension of steel strings which produce a brighter tone, and according to some players, a louder sound. The acoustic guitar is a staple in folk, Old-time music and blues. Archtop guitars are steel string instruments which feature a violin-inspired f-hole design in which the top (and often the back) of the instrument are carved in a curved rather than a flat shape. Lloyd Loar of the Gibson Guitar Corporation invented this variation of guitar after designing a style of mandolin of the same type. The typical Archtop is a hollow body guitar whose form is much like that of a mandolin or violin family instrument and may be acoustic or electric. Some solid body electric guitars are also considered archtop guitars although usually 'Archtop guitar' refers to the hollow body form. Archtop guitars were immediately adopted upon their release by both jazz and country musicians and have remained particularly popular in jazz music, usually using thicker strings (higher gauged round wound and flat wound) than acoustic guitars. Archtops are often louder than a typical dreadnought acoustic guitar. The electric hollow body archtop guitar has a distinct sound among electric guitars and is consequently appropriate for many styles of rock and roll. Many electric archtop guitars intended for use in rock and roll even have a Tremolo Arm.

Resonator, resophonic or Dobro guitars: Similar to the flat top guitar in appearance, but with sound produced by a metal resonator mounted in the middle of the top rather than an open sound hole, so that the physical principle of the guitar is actually more similar to the banjo. The purpose of the resonator is to amplify the sound of the guitar; this purpose has been largely superseded by electrical amplification, but the resonator is still played by those desiring its distinctive sound.
Resonator guitars may have either one resonator cone or three resonator cones. Three cone resonators have two cones on the left above one another and one cone immediately to the right. The method of transmitting sound resonance to the cone is either a BISCUIT bridge, made of a small piece of hardwood, or a SPIDER bridge, made of metal and larger in size. Three cone resonators always use a specialised metal spider bridge.

The type of resonator guitar with a neck with a square cross-section -- called "square neck" -- is usually played face up, on the lap of the seated player, and often with a metal or glass slide. The round neck resonator guitars are normally played in the same fashion as other guitars, although slides are also often used, especially in blues.