The Glimmerglass Festival is an American opera company. Founded in 1975 by Peter Macris, the Glimmerglass Festival presents an annual season of operas at the Alice Busch Opera Theater on Otsego Lake eight miles (13 km) north of Cooperstown, New York, United States. The summer-only season usually consists of four productions performed in rotating repertory. Glimmerglass is well known for producing new, lesser-known, and rare works, many of which in years past have been co-produced with the New York City Opera. It is the second-largest summer opera festival in the United States, currently led by artistic and general director Robert Ainsley, who succeeded Francesca Zambello in 2022.

L'assedio di Calais is an 1836 melodramma lirico, or opera, in three acts by Gaetano Donizetti, his 49th opera. Salvatore Cammarano wrote the Italian libretto, which has been described as "...a remarkable libretto, the closest Cammarano ever got to real poetry, particularly in his description of the embattled city and the heartfelt pride of its citizens". It was based on Luigi Marchionni's play L'assedio di Calais, which had been presented in Naples around 1825, and secondarily on Luigi Henry's ballet L'assedio di Calais, which had been performed in Naples in 1828 and revived in 1835.