The Well-Tempered Guitars began to take shape at the beginning of March 1962, when the performances of the French guitar duo formed by Ida Presti and Alexandre Lagoya aroused great enthusiasm in the Californian musical community. The preludes and fugues were the most admirable result of an intense and concentrated period of composition to which the Sonatina Canonica Op. 196 (1961) and the Concerto Op. 201 (1962) also belong. The speed of the composer in the creation was prodigious: less than three months of disciplined work for more than two hundred pages of score. The first of the four books into which the cycle is subdivided was completed between 8 and 27 March; Castelnuovo-Tedesco worked on the second between 23 and 11 May, after a pause of more than three weeks; the third book bears the dates of 14 and 26 May, and the last, begun on the 22 May, was completed on 3 June 1962.  Similarly to the two books of the Bach model of reference (The Well-Tempered Clavier), the twenty-four preludes and fugues for the guitar are written in all the major and minor keys. For an instrument that rarely and reluctantly departs from the close context of the usual keys, it was an ambitious challenge, taken up by the composer who in his youth, as an enthusiastic composition student of Ildebrando Pizzetti, had set himself the task of writing three hundred and sixty-five fugues in a year one a day with the purpose of perfecting his command of counterpoint. The series of keys moves forward in ascending fifth intervals, stating from G minor and alternating rigorously between preludes and fugues in a minor key and preludes and fugues in a major key: a different and original solution from the Well-Tempered Clavier (in which the progression of the keys takes place by ascending semitones) and texts like the 24 Preludes Op. 28 by Chopin or the 24 Preludes and Fugues Op. 87 by Shostakovich, where the major keys are certainly organized according to the cycle of ascending fifths, but always coupled with their respective minor key.