For many people, their first images of guitars are acoustic guitars, perhaps one owned by a friend or an older sibling. From campfires to concert halls, acoustics have helped define the sound of many styles of music, especially folk and country, though many blues, pop, and rock artists have used acoustic instruments as the foundation of their sound as well. Due to the variety of different sounds available from different guitars, the acoustic has found its place in a wide range of musical genres.
Acoustic-type guitars are popular first instruments with many beginning guitarists because they are self-contained, i.e. no amplifier is required for them to produce sound. You don't have to worry about purchasing an amplifier - you can practice in the back yard as easily as you can a dorm room.
Because of their capacity for a softer sound, acoustics are popular with folk musicians (such as Peter, Paul, and Mary) and country artists, although country guitarists have to be versatile enough to switch from acoustic to electric as needed.
One popular misconception is that you play an acoustic differently from an electric. While the sounds they produce and the techniques used are different, acoustic and electric guitars are tuned and played the same. If you learn on an acoustic, you can play an electric and vice-versa.
Since the 1980s, acoustic/electric models have become popular, where the acoustic sound is preserved yet the instrument is able to be amplified to make up for its low volume (though feedback problems sometimes present themselves). Acoustic/electric models are usually available as cutaway models, allowing easier access to the upper frets, often necessary for lead lines.
Perhaps even more so than electric guitars, the sound of acoustic instruments depends upon the type of wood used in its construction. For example, a guitar with a maple top will sound far different than a guitar with a cedar top, the former having a brighter sound with the latter having a warmer, more mellow sound. Because of their construction, acoustics are also far more sensitive to humidity than electrics, though simple measures can be taken to protect guitars from excessive or insufficient humidity, such as in-case humidifiers and room humidifiers set to 45% humidity (or thereabouts).
While in the past it was difficult to purchase a decent acoustic for less than several hundred dollars, the rise of quality offshore manufacturing coupled with the dependency of computerized routers (CNC machines) has allowed many companies to produce fine acoustic instruments for an affordable price. Because acoustic instruments generally have higher action (i.e. the strings are higher off of the fretboard), poor quality instruments can be incredibly difficult to play. Fortunately, it's relatively easy these days to find good-playing instruments for little money.
Acoustic Guitar Companies