This edition of Messa da Requiem is based on Verdi's autograph score and other authentic sources. The appendixes include two pieces from the compositional history of the Requiem: an early version of the Libera me, composed in 1869 as part of a collaborative work planned as a memorial to Rossini; and the Liber scriptus, which in the original score of the Manzoni memorial Requiem was composed as a fugue in G minor. The introduction to the score discusses the work's genesis, instrumentation, and problems of notation, while the critical commentary discusses the editorial decisions and traces the complex compositional history of the Requiem.