Universally known as the "Sonata facile (or semplice)," the relative ease of K. 545 has ensured that it has become the most of famous of all Mozart's piano sonatas, a work that scarcely a student of the instrument fails to learn at some point in his or her career. The entry in Mozart's own thematic catalog, dated June 26, 1788, adds that the sonata was intended "for beginners." Yet despite its fame today, the circumstances of its composition are not known, the original manuscript is lost, and the sonata was not published in Mozart's lifetime, the first edition appearing in 1805 from the press of the composer and publisher Johann André of Offenbach.

There are three short movements: an Allegro, often quoted as a paradigm of the ambiguity of Classical "simplicity," a charming central Andante, and a tiny finale in Rondo form. It is remarkable to note that this unpretentious little work must have been composed at the same time as the great last trilogy of symphonies; indeed it was added by Mozart to his catalog of works on the same day as the first of those magnificent works, the great Symphony No. 39 in E flat, K. 543, one of his grandest conceptions.

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