Besides writing for the concert hall, Glass continued his ongoing operatic series with adaptions from literary texts: "The Marriages of Zones 3, 4 and 5" ( story-libretto by Doris Lessing), "In the Penal Colony" (2000, after the story by Franz Kafka), and the chamber opera "The Sound of a Voice" (2003, with David Henry Hwang), which features the Pipa, performed by Wu Man at its premiere. Glass also collaborated again with the co-author of "Einstein on the Beach", Robert Wilson, on "Monsters of Grace" (1998), and created a biographic opera on the life of astronomer Galileo Galilei (2001).