By the end of the Baroque period, two significant changes had occurred. The guitar's five courses were replaced by six single strings, and they were tuned in the modern style of EADGBE.

Many changes were taking place musically by this time. The modern piano made its first appearance, and the guitar began to fade from popularity. It was soon considered a more frivolous instrument of seduction and amour. A German diarist wrote, “The flat guitar with its strum we shall happily leave to the garlic-eating Spaniards.”

In 1799, Fernando Ferrandiere published a method book for the six-string guitar called The Art of the Spanish Guitar. In that same year, Don Federico Moretti wrote the first standardized book on the six-string guitar, The Principles of Playing the Guitar with Six Strings. Guitar scholars believe both method books were derived from an earlier publication by guitarist Antonio Ballesteros, titled Obra para Guitarra del sexto orden.

Romance, lasciviousness, and the guitar have been fairly consistent partners for a while, not just in the modern age of heavy-metal rockers. For example, Ronsard, a famous fifteenth-century French poet, wrote:

It is the ideal instrument

For ladies of great learning,

Lascivious ladies also play

To advertise their yearning.

Gaspar Sanz, guitarist to the viceroy of Aragon, Spain, was as much a philosopher as a musician. His comments about the instrument and its players stand as well today as they did when he wrote the introduction to his method book on the guitar in the late seventeenth century: “[The guitar's] faults … lie in whoever plays it, and not in the guitar itself, for I have seen some people accomplish things on one string for which others would need the range of an organ. Everyone must make of it what he can, good or bad.”

The Napoleonic war, at the turn of the nineteenth century, was responsible for making the guitar popular again. The war, which raged throughout Europe, reintroduced Europeans to the guitar-based music of Spain. This period led to the work of such composers and performers as Fernando Sor, Mauro Guilliani, Matteo Carcassi, and Ferdinando Carulli.

The first modern concerto for guitar and orchestra, “Concerto No. 1 in A Major,” was composed and performed by the Italian virtuoso Mauro Guilliani. Among other things, it uses the right-hand thumb for bass notes and features a strong orchestral structure, with variations on a theme, a slow second movement, and finally a lively third movement.