I can think of no better way of opening this section than with excerpts from "The Guitar - the Definitive Reference" by Terence Ashley, which I highly recommend to the beginning student or anyone else interested in the guitar and music in general (this work is available on line and I've included it in the list of suggested reading):

The name of Antonio de Torres Jurado is well known to any serious student of the classical guitar. More than any other maker before or since, he modernized the instrument, vastly improving its tone and at the same time increasing the sheer amount of sound that could be produced on it. This enabled guitarists to be heard as part of larger ensembles and also to play in larger concert halls. The richness of tone inspired ever more composers to write for the instrument and thus helped to increase its repertoire.
Torres was responsible for increasing the overall size of the guitar, and determined that the scale length - the distance from the nut, at the top of the neck, to the bridge, near the back of the soundboard - Should be 65 cm (25.6 in). He took the fan-struts idea of Pagés and Benedid and improved on it, placing seven struts, laid out in the shape of a fan, behind the sound hole - to distribute the vibrations from the bridge better - and a further two struts at a tangent to the fan. Torres also introduced a bridge saddle to which the strings were tied after passing over the bridge, an arrangement that is still the norm for guitars built today.
As the lute makers of old had discovered, by using struts it was possible co "break up" the surface area of the soundboard. This had the double benefit of introducing extra rigidity to the thinnest parts of the guitar (allowing the delicate soundboard to be made even thinner) while also raising the resonant frequency of the instrument. This meant that far more of the supporting harmonics of the fundamental note were produced when the strings were plucked, producing a noticeably richer tone on the instrument. The increase in size of the guitar also made it a lot louder.
Put simply, the extra space inside the body increased the amount of air being shifted as the soundboard vibrated, causing a louder sound to be emitted. Antonio de Torres was the father of the modern classical guitar. Many very fine instruments have been built since his death, but they all owe a debt to Torres' pioneering work, He was succeeded in Spain by a generation or two of very fine guitar makers, men such as Manuel and José Ramirez. The Ramirez company survives to this day, and continues to make some of the most sought-after instruments in the world.

The renewed interest in the classical guitar in the twentieth century saw the arrival of new, non-Spanish guitar makers on the scene. The quality of their work is such that it can now be said with some degree of certainty that the best classical guitars are no longer made in Spain. Chief among these new makers are Hermann Houser in Germany, Robert Bouchet in France, David Rubio and Paul Fisher in England and father-and-son partnership John and
William Gilbert in America.
These makers are able to take advantage of a range of woods that would have been undreamed of in Torres' day. A typical modern quality classical guitar maker might choose to use Brazilian or Indian rosewood for the back and sides of the instrument and Brazilian rosewood for the neck. The sides and the soundboard would be anchored to a piece of South American mahogany or cedar wood and the fingerboard would be made of ebony from Ceylon. The head might well be decorated with a veneer of South American snakewood and the all-important soundboard made from Alpine spruce, which is specially grown at high altitude.
Once all of this wood has been seasoned - a process which involves storing it under controlled conditions while it dries out and ceases to move around - the maker can begin construction of the instrument, a process which usually takes well over one hundred hours of intensive, hands-on work. The first stage in this process involves creating the characteristic shape of the neck. Slots are cut into the sides of the base of the neck, at the point where the
twelfth fret will be once the fretboard has been added. The sides of the instrument, which are around 2 mm (0.08 in) thick, will have been given their waisted shape by steam-bending them and clamping them to a mould. Once this process has been completed, one end of each side will be placed in one of the slots on the neck and the other end fixed to a solid block of a hard wood such as mahogany or cedar. This piece of wood, called the end block,
provides a vital anchor point for the various components that go to make up the body of the guitar. The back of the instrument is then attached. It usually consists of two pieces of matched hardwood, which are cut into shape and joined down the middle. At one end the pieces connect to the end block and at the other they are fixed
to what is known as the "toe" of the neck. A thin strip of wood called a cleat is then fixed along the join on the inside of the instrument. This run for the entire length of the back of the body and serves to seal the join between the two pieces of wood that make up the back of the instrument. The back is then fixed to the sides by means of a strip of wood which had been "kerfed" (slit or scored) to make it more pliable and therefore easy to fit inside the contours of the instrument.
The soundboard, with its various struts already attached, is then fitted to the rest of the body of the guitar, once again being joined at the neck and to the end block, as well as to the sides of the instrument. Then the fingerboard is fitted to the neck and body, the bridge is glued on to the soundboard and the ornate "purfling" around the perimeter of the body is fixed on.(The rosette around the sound hole is normally attached when the soundboard is being constructed.) At this point the instrument receives its finish - layers of varnish or French polishing of the wood.
An astonishing degree of variation in tonal colour and sound characteristics such as volume response can be achieved through the use of different woods or by changing key elements of the instrument's construction. Virtually every
component part of the guitar will have some bearing on the volume, tone and sustain of the finished instrument. The flamenco guitar, for instance, bears it superficial resemblance to the classical guitar, but is made using different woods, has it thinner soundboard, a shallower body and is generally of a much lighter construction. This is for creating the particular tonal characteristics that one associates with the flamenco guitar - warmer tone, greater attack and a stronger but shorter sustain. The guitar maker's art is in achieving a balance between these properties in order to produce a fine instrument. Learning how to combine and control all of these elements constitutes a life's work, and so even those guitarists who can afford a instrument made by an established and respected guitar maker may have to wait quite some time before getting their hands on one.
In terms of outward appearance, the guitar has changed little in the last hundred years. However, beneath the surface the of the soundboard all kinds of changes have been taking place. Torres's struts are still there, but they now run in parallel along the grain of the soundboard. By strengthening the internal bracing, it has been possible to cut clown the amount of vibration occurring within the body of the instrument, allowing more of the guitar's sound to be heard as it is projected more efficiently than ever before.

The changes in the guitar has been constructed, and therefore the way it sounds and responds, has led to a number of changes in the way the instrument is played. These can roughly be dated as beginning around the time when Torres launched his guitars at the world, although the actual changes in technique can be credited, in the first instance, to Francisco Tárrega, one of the world's leading guitarists toward the end of the nineteenth century.
Tárrega, by means of the floating-arm technique mentioned earlier, established the apoyando stroke. This had the double benefit to the player of being louder than the conventional tirando stroke (which was used almost exclusively at this time) and also of helping to bring out more of the richer qualities of these new instruments. The Torres guitar was bigger than had been the norm, up to this point and as such fitted more comfortably across the left thigh -
before, guitarists would just as often sit with the instrument placed over the right thigh. It became standard practice to sit with the classical guitar over the left thigh and remains so.
Although Tárrega did not play the guitar using the fingernails of his right hand, several of his students did and so this technique was passed down to succeeding generations of guitarists. At this time, however, the right hand position had not been formalized and it was not until the twentieth Century that Andrés Segovia established the practice of playing with a relaxed right hand and striking the strings with the left-hand side of the fingernails. Interestingly, a very small number of concert players favor the right-hand side of the fingernail and so adapt their technique accordingly.

The evolution of the modern classical guitar tradition can be traced back to European folk and other "low-brow" musical forms, all of which created a view among the upper classes that the guitar was a "common" instrument not worthy of serious attention. Although it now has broad parity with other traditional classical instruments, its greatest asset has been its enduring significance as an unashamedly populist instrument - indeed, the guitar was at the very heart of much of the non-classical music of the twentieth century, from folk, country, and jazz to rock and pop.
This line of popular heritage stems mainly from developments by European immigrants in the United States.
For while a classical revolution was taking place in Spain during the nineteenth century, history was also being forged in America, where two distinct styles were being developed by two of the most significant figures in guitar history: C F Martin, maker of guitars with traditional, flat soundboards, and Orville Gibson, who developed archtop guitars with curved fronts in the tradition of violin making.

Hailing from a long line of musical instrument makers, Christian Frederick Martin was born in 1796 in Germany. At the age of 15 he left home for Vienna where he became an apprentice to the noted luthier Johann Stauffer. By all accounts Martin was an eager, motivated worker who within a few years had become a master craftsman and factory foreman. In about 1820, after marrying, he returned to his home town to open up his own guitar-manufacturing business. However, shortly after his return, Martin quickly became embroiled in a bitter dispute between rival guilds. The Martin family had been long-standing members of the cabinet makers' guild, whose craftsmen had traditionally built lutes and guitars. In an effort to restrict competition, the violin makers' guild argued that, as supposedly inferior craftsmen, the cabinet makers ought not to be allowed to make any musical instruments.
The cabinet makers cited the importance of the work of Georg Martin and his son Christian in the development of the guitar. It was testimony from a noted wholesaler, who declared that Martin 11 produced guitars which in point of quality and appearance leave nothing to be desired and which mark him as a distinguished craftsman," that finally won the battle for the cabinet makers. Martin was allowed to stay in business, but was disillusioned by the experience and decided to start again from scratch in America.
Arriving in New York City in 1833, Martin opened a modest music store which housed a small guitar production workshop in the back room. At this time there was little widespread demand for guitars in America and to make ends meet early makers sometimes bartered their instruments for food and wine. After six years of life in New York City - a place that Martin had never much liked - he sold his store to buy eight acres of land on the out-skirts of Nazareth, Pennsylvania. Turning his back on retailing, Martin concentrated his efforts solely on the production of his musical instruments.Martin's first guitars were hand-crafted to order, and showed little standardization. They were, however, strongly reminiscent of the classical instruments he built for Stauffer back in Vienna, most notably in the headstock design which positioned all the tuning pegs on one side. Although this approach was abandoned after C F Martin's death in 1873, the idea influenced later solid-body designers such as Paul Bigsby and Leo Fender. An unusual feature
of the early Martin guitars was the adjustable neck, the tilt of which could be altered by means of a clock key fitted into the heel - the joint between the neck and the body. During the 1890s, when steel strings began gradually replacing those made from gut, this system was dropped because steel strings exerted greater stress
on the neck fixture.
During the 1850s C F Martin made one of his most important design innovations - the development of the cross-bracing system fitted to the underside of the soundboard. This was a pattern of struts which gave the instruments a distinctive treble tone. By the turn of the turn of the century the majority of steel-string guitar makers used variations on this system.