• Francesco Cavalli. Drama musicale in a prologue and three acts. 1648.
• Libretto by Giacinto Andrea Cicognini, after the Argonautica of Apollonius Rhodius.
• First performance at the Teatro S Cassiano, Venice, on 5th January 1649.

As in a number of other operas of the period, the prologue shows gods in dispute. Here Apollo favours Medea and Cupid her rival, Hypsipyle, in their liaisons with Jason. It is evident that Jason and his crew, the Argonauts, have spent a considerable time in Colchis in their quest for the Golden Fleece, since he has already fathered twins on Medea, but is unaware of her identity. He promises to marry her. Jason's wife, and mother of twins, Hypsipyle, comes in search of him, resolving, once she knows of his infidelity, to kill her rival, while Medea uses her magic powers to help Jason. He, successful in seizing the Golden Fleece, sets sail with Medea for Corinth, followed by Aegeus, Medea's unsuccessful suitor, and his stuttering comic servant Demo. Hypsipyle eventually finds Jason and reproaches him, but he disowns her, as deluded. He later gives orders to his Captain, Besso, to have her killed, telling her, as a password, to ask if his orders have been carried out. Medea, checking on the planned death of her rival, seeks out Besso and asks the same question, with results immediately fatal, had not Aegeus appeared to save her. Jason is saved from death at the hands of Aegeus by the intervention of Hypsipyle and when Medea re-appears, now miraculously saved, a happy ending is possible, with Jason and Hypsipyle again united, and Medea now happy to accept the attentions of Aegeus.

Giasone, with its mixture of comedy and more serious elements, enjoyed the widest popularity. The mixture had become a part of the genre, as in Monteverdi's L'incoronazion di Poppea in 1643. Its separation of aria and recitative marks a new stage in operatic development, a change from the earlier practice of arioso , the use of recitative with passages of more melodic appeal, as words and drama dictated. Now narrative and action made use of recitative, while arias allowed reflection on what had happened or revelations of feelings of a character. The plot used is very different from that of the play by Euripides, the basis of other operas, which ends in spectacular murder and tragedy.