Today's classical and flamenco guitar are both derived from the pattern conceived in Spain in the mid-nineteenth century by Antonio de Torres of Seville and Almeria. His essential design for the shape (or plantilla), bracing, scale length, and decoration displaced the other styles of European guitar of the time and has prevailed through the years.
The sound of the Spanish guitar pushed the popularity of the instrument further, as it carried better in larger halls. Flamenco music also benefitted as the guitar became more audible alongside singers and the stamping of dancers, thus spawning a new kind of flamenco player, who used the guitar as a solo instrument.
Sometime in the 1920s and 30s, guitar makers and players started differentiating between the form of flamenco guitar and classical or concert guitar. This was mostly because of players such as Andrés Segovia who standardized the repertoire and technique for playing baroque, romantic and classical music, and Ramón Montoya who did the same for virtuoso flamenco music.
The classical guitar tends to be made of rosewood, be heavier, have more sustain and have higher action. The traditional flamenco guitar is usually made of cypress, is very lightly built, has a percussive and quick sound, has low action, and usually has wooden friction pegs. From the 1970s, some top flamenco players started using guitars made of rosewood and standard tuning machines. This guitar is called flamenco negra, while the cypress one, flamenco blanca. The rosewood body gives the flamenco sound a little more sustain.
The Spanish guitar also became very popular in Latin America, were it was seen as a cultured instrument. Apart from classical and Spanish music, ballads, boleros, rancheras, tangos, valses, milongas, andean and other rhythms were mostly played on Spanish guitar. The composer Agustín Barrios Mangoré, from Paraguay, is considered one of the most important, adding many pieces to the repertoire. So is the Brazilian composer Heitor Villa-Lobos. In Brazilian popular music, or MPB, it is also used extensively, mainly for bossa nova.
Though the design has remained virtually unchanged for the last 150 years, it has enjoyed a variety of interpretations by all the important makers of the instrument. Experiments with the structure, materials, and the look have been well appreciated and in many cases have marked some definite improvements in sound or loudness of the guitar, yet there are many who cling to the traditional Spanish way, and consider it the only way.