The primary characteristics of a steel-string acoustic guitar are self-evident from the name. At first glance or from a distance, it appears completely similar to the traditional classical, or Spanish, guitar. However, closer inspection reveals that the strings, rather than being nylon, are steel, and there is no mistaking the sound of a steel-string for that of a classical instrument. Devotees of the steel-stringed guitar are usually drawn to that sound, which is "brighter" and louder than that of its classical cousin.

The steel-string acoustic guitar, as mentioned, very closely resembles the classical guitar in basic shape. Both instruments typically sport six strings, although twelve-string variations are not uncommon. However, the steel-string guitar usually has a larger sound box and heavier construction overall. This is because steel strings require a higher tension level than those made of nylon; a classical guitar has a string tension of 75-90 pounds, whereas a steel-string guitar has a string tension of 150-200 pounds. Accordingly, the construction of the steel-string guitar must be able to withstand the increased tension. The steel-string guitar also uses a different bracing system for the strings, which is called "X-bracing," whereas classical guitars typically use a style called "fan bracing."

Steel-string acoustic guitars can be made from a variety of different woods, including spruce, maple, mahogany, and rosewood. More expensive instruments will feature sides, backs, and tops made from a solid "tonewood," which is a wood possessing consistent acoustic qualities. The least expensive models are usually made entirely of laminated wood, and mid-range instruments combine the two approaches. The necks of these guitars are usually made of mahogany and the fretboards of a dense tropical hardwood such as ebony. Because steel-string guitars are almost always made of several different types of wood, there is a great deal of potential for variation in the instruments' timbre, or "tone." Certain design and construction elements are influential factors as well.

Interestingly, there has been a recent trend toward experimentation with alternate types of materials in the construction of steel-string acoustic guitars. This trend has been driven by a sharp decrease in availability and a simultaneous rise in price of those species of wood traditionally used. For example, some makers have begun to producing models with tops made of red cedar, plastic, or even graphite. Although there are numerous producers of steel-string acoustic guitars, the most prominent in the United States are probably the Guild Guitar Company, C.F. Martin & Company, and Gibson Guitar Corporation.

The traditional territories of the steel-string acoustic guitar have been blues, country, bluegrass, folk, and certain genres of rock. However, since ever since the "sex, drugs, and rock and roll" era of the 1960s, this instrument has begun to crop up in an ever-wider array of music genres. The music now played on the steel-string acoustic guitar has influences from all countries and time periods, from Celtic to classical European to traditional Indian. Today, those in the pop music industry will generally select the steel-string guitar over classical. Famous artists such as Eric Clapton and bands like The Eagles have helped cement the steel-string guitar's place in the music industry.