At the time when Calderon began to compose for the stage, the Spanish drama was at its height. Lope de Vega, the most prolific and, with Calderon, the greatest, of Spanish dramatists, was still alive; and by his applause gave encouragement to the beginner whose fame was to rival his own. The national type of drama which Lope had established was maintained in its essential characteristics by Calderon, and he produced abundant specimens of all its varieties. Of regular plays he has left a hundred and twenty; of "Autos Sacramentales," the peculiar Spanish allegorical development of the medieval mystery, we have seventy-three; besides a considerable number of farces. 

The dominant motives in Calderon's dramas are characteristically national: fervid loyalty to Church and King, and a sense of honor heightened almost to the point of the fantastic. Though his plays are laid in a great variety of scenes and ages, the sentiment and the characters remain essentially Spanish; and this intensely local quality has probably lessened the vogue of Calderon in other countries. In the construction and conduct of his plots he showed great skill, yet the ingenuity expended in the management of the story did not restrain the fiery emotion and opulent imagination which mark his finest speeches and give them a lyric quality which some critics regard as his greatest distinction.

Of all Calderon's works, "Life is a Dream" may be regarded as the most universal in its theme. It seeks to teach a lesson that may be learned from the philosophers and religious thinkers of many ages—that the world of our senses is a mere shadow, and that the only reality is to be found in the invisible and eternal. The story which forms its basis is Oriental in origin, and in the form of the legend of "Barlaam and Josaphat" was familiar in all the literatures of the Middle Ages. Combined with this in the plot is the tale of Abou Hassan from the "Arabian Nights," the main situations in which are turned to farcical purposes in the Induction to the Shakespearean "Taming of the Shrew." But with Calderon the theme is lifted altogether out of the atmosphere of comedy, and is worked up with poetic sentiment and a touch of mysticism into a symbolic drama of profound and universal philosophical significance.