opera seria (It.). Serious opera. In the 17th and 18th cents., opera seria was the chief operatic genre, becoming very formal and complex, with elaborate display arias. Mythological subjects were the norm, and most of these were written for various composers by the librettist Metastasio. The last and greatest examples of the form were Mozart's Idomeneo (1781) and La clemenza di Tito (1791).

opera seria Style of Italian opera in the 17th and early 18th centuries. The plots were usually heroic or tragic. Priority was given to virtuoso vocal display in elaborate arias. The formalism and stylization of such operas prompted a reaction that gave rise to the development of opera buffa.