Così fan tutte, ossia La scuola degli amanti (Thus Do They All, or The School for Lovers) K. 588, is an Italian-language opera buffa in two acts by Wolfgang Amadeus Mozart first performed in 1790. The libretto was written by Lorenzo Da Ponte, who also wrote Le nozze di Figaro and Don Giovanni.

Although it is commonly held that Così fan tutte was written and composed at the suggestion of the Emperor Joseph II, recent research does not support this idea. There is evidence that Mozart's contemporary Antonio Salieri tried to set the libretto but left it unfinished. In 1994, John Rice uncovered two terzetti by Salieri in the Austrian National Library.

The title, Così fan tutte, literally means "Thus do all " and is popularly used to mean "Women are like that". The words are sung by the three men in act 2, scene 3, just before the finale. Da Ponte had used the line "Così fan tutte le belle" earlier in Le nozze di Figaro (in act 1, scene 7).

The first performance of Mozart's setting took place at the Burgtheater in Vienna on January 26, 1790. It was given only five times before the run was stopped by the death of the Emperor Joseph II and the resulting period of court mourning. It was performed twice in June 1790, with the composer conducting the second performance, and again in July (twice) and August (once). After that it was not played in Vienna during Mozart's lifetime. The first British performance was in May 1811, at the King's Theatre, London. Così fan tutte was not performed in the U.S. until 1922, when it was given at the Metropolitan Opera

According to William Mann, Mozart disliked prima donna Adriana Ferrarese del Bene, da Ponte's arrogant mistress for whom the role of Fiordiligi had been created. Knowing her idiosyncratic tendency to drop her chin on low notes and throw back her head on high ones, Mozart filled her showpiece aria Come scoglio with constant leaps from low to high and high to low in order to make Ferrarese's head "bob like a chicken" onstage.

The subject matter (see synopsis below) did not offend Viennese sensibilities of the time, but throughout the 19th and early 20th centuries it was considered risqué. The opera was rarely performed, and when it did appear it was presented in one of several bowdlerised forms.

After World War II, it regained its place in the standard operatic repertoire. It is frequently performed and appears 14th on the Operabase list of the most-performed operas worldwide.

Louis Nowra uses the staging of Così fan tutte in a mental hospital as a background for his 1992 play Così.