The Pianoduo Festival Amsterdam runs from Thursday 8 to Sunday 11 October at several venues across the city.
A piano duo is two pianists playing one or two pianos, while quatre-mains, meaning four hands, is two players sharing one instrument.
The genre is rarely programmed in concert halls, which is why the festival champions it.
At one keyboard both players shape the music, and the lead passes back and forth as the musical line moves between them.
They stay together through small signals such as a breath, a movement or a glance, because the slightest delay or rush is heard at once.
Many composers wrote for these line-ups, especially in the nineteenth and twentieth centuries.
Classics include Schubert’s Fantasie in F, Mozart’s Sonata in D, KV 448, and Brahms’s Hungarian Dances, which are usually heard in orchestral versions but were first written for piano four hands.
Stravinsky, Bartók and Ligeti later wrote for the format too.
Four-hand playing once gave two people a rare chance to sit close together in public, and Schubert dedicated his Fantasie to his pupil, Countess Caroline Esterházy.
For more live classical music, check out our guide to the city’s concert halls and music stages.