The Peel Commission (1936–37) was the first British commission of inquiry to recommend the partition of Palestine into two states. The commissioners made their recommendation after listening to several weeks of testimony, delivered in both public and secret sessions. The transcripts of the public testimony were published soon afterward, but the secret testimony transcripts were only released by the United Kingdom’s National Archives in March 2017. Divided into two parts, this article closely examines the secret testimony. Part I discusses how the secret testimony deepens our understanding of key themes in Mandate history, including: the structural exclusion of the Palestinians from the Mandate state, the place of development projects in that structural exclusion, the different roles played by British anti-Semitism and anti-Arab racism, and the importance of the procedural aspects of committee work for understanding the mechanics of British governance. Part II extends this analysis by focusing on what the secret testimony reveals about how the Peel Commission came to recommend partition.