I puritani (The Puritans) is an 1835 opera by Vincenzo Bellini. It was originally written in two acts and changed to three acts before the premiere on the advice of Gioachino Rossini, with whom the young composer had become friends. The music was set to a libretto by Count Carlo Pepoli, an Italian émigré poet whom Bellini had met at a salon run by the exile Princess Belgiojoso, which became a meeting place for many Italian revolutionaries. The opera is based on Têtes Rondes et Cavaliers (Roundheads and Cavaliers), a historical play written by Jacques-François Ancelot and Joseph Xavier Saintine and set in the English Civil War. Except for its title, the opera is not in any way based on Walter Scott's 1816 novel Old Mortality (translated into Italian in 1825 as I Puritani di Scozia), despite some claims to the contrary.

When Bellini arrived in Paris in mid-August 1833, he had intended to stay only about three weeks, the main aim being to continue the negotiations with the Paris Opéra which he had begun on his way to London a few months earlier. These negotiations came to nothing, but by October he had decided to spend the winter in Paris, especially as both Il pirata and I Capuleti e i Montecchi were to be given by the Théâtre-Italien that season. The offer from the Théâtre came in January 1834; he accepted because "the pay was richer than what I had received in Italy up to then, though only by a little; then because of so magnificent a company; and finally so as to remain in Paris at others' expense."

Taking from April until its premiere the following January, Bellini had time to ensure that the opera was as close to perfection as possible. After the premiere, Bellini reported to his friend Francesco Florimo in Naples that:

The French had all gone mad; there were such noise and such shouts that they themselves were astonished at being so carried away ... In a word, my dear Florimo, it was an unheard of thing, and since Saturday, Paris has spoken of it in amazement

It was to be Bellini's final work; he died in September 1835 at the age of 33.

Upon his arrival in Paris, Bellini quickly entered into the fashionable world of the Parisian salons, including that run by Princess Belgiojoso whom he had met in Milan. In addition to the many writers of the time, among the musical figures which he would have encountered were several Italians such as Michele Carafa and Luigi Cherubini, then in his seventies. Thus, for most of the remainder of 1833, Bellini's musical activity was very limited. He pleaded guilty in the letter to Florimo in March 1834 noting that the city's attractions were immense.

The contract to write a new opera for the Théâtre-Italien, which was signed in January 1834, called for it to be presented at the end of that year. Once it was signed, Bellini began to look around for a suitable subject and, in a letter to Florimo of 11 March 1834, he expresses some frustrations, noting: "I am about to lose my mind over the plot of the opera for Paris, as it has been impossible to find a suitable subject for my purpose and adaptable to the company".

In the same letter he tells of working towards finding a subject with the Italian émigré, Count Pepoli, who had not written a libretto before. However, on 11 April he is able to say in a letter to Ferlito that he was well and that "I have chosen the story for my Paris opera; it is of the times of Cromvello [Cromwell], after he had King Charles I of England beheaded." The chosen source of the libretto was identified as a play performed in Paris only six months before in September 1833. When first shown the play and other possible subjects by Pepoli, in the opinion of writer William Weaver, "it was clearly the heroine's madness that attracted the composer and determined his choice.