Othello lasts only one night. It starts in Venice, where Othello secretly marries the daughter of a nobleman (Desdemona). Together they go to explore Cyprus. Here, Iago tells his plan to separate the two lovers, indeed he succeeds in making Othello believe Desdemona really loves Cassio. Then, because of his jealousy, Othello kills Iago's wife, and kills Desdemona. Only later he discovers Iago's plan, so he decides to kill himself while Iago is imprisoned and Cassio becomes the Governor of Cyprus.
Othello is based on a jealousy story written by the writer Giraldi Cinzio, but is different because the Italian Othello is a man without dignity, while Shakespeare's Othello has many qualities. Italy, and in particular Venice, was considered by Elizabethans as immoral, so Venice was chosen when people wanted to represent immorality with its easily-jealous men and beautiful women.
Othello is a good man, he believes in real values and feels true emotions. On the contrary, Iago is a false person, a villain who plots to express is power, a loser who invents false emotions. Desdemona is presented as a simple object of desire and jealousy. Her love for Othello is so sincere that she lets herself be guided from his lover. She's described by Iago with his vulgar remarks and by Othello with his praises about her beauty and innocence.
The jealousy is the main theme, it moves the whole play. Another theme is that of the opposition: Othello and Desdemona's love that triumphs over cultural differences and Othello's ingenuity, but also for the contrast between Othello and Iago, two opposite poles.
This play is the most perfectly constructed of all Shakespeare's tragedies. He uses four different kinds of dramatic speech (lyric poetry, rhyme, blank verse and prose) and two different styles of language.