The Acte de ballet "Zéphire" was never performed during the lifetime of its authors, although the autograph manuscript shows traces that Rameau worked on it several times between 1748 and 1759 – possibly with a view to performances that did not materialize? The introduction to this volume of the Complete Edition examines in detail the many unanswered questions regarding the dating, the attribution of the unknown librettist, the circumstances of the composition and the hypotheses in this regard. The edition argues that the structure of the libretto of "Zéphire" reflects Louis de Cahusac's principles, as, similar to "Les Fętes de Polymnie" and later "Les Fętes de l'Hymen et de l'Amour", the score features numerous dances and choruses that are closely interwoven into the plot. Cahusac, who saw the imitation of nature as the essence of art, liked to provide precise stage directions for choral and ballet interludes; this is also the case in "Zéphire". The subject of the libretto goes back to the legend of Zephyr and Flora, as depicted by Ovid in the fifth book of his Roman festival calendar "Fasti". Zéphire, the god of the west wind, loves Chloris, a forest nymph of the goddess Diana. Eventually, the lovers win the favour of the feared goddess, and Zéphire transforms Chloris into Flora, the goddess of spring. This critical edition is based on the undated autograph and a copy by the copyist Serre from 1777, whereby the autograph manuscript contains various layers of composition; these earlier layers are reproduced in five appendices as far as they can be reconstructed.