The reproduction of Alan Turing’s letters and papers has been made possible by the kind permission of the Fellows and Scholars of King’s College, Cambridge, the A.M. Turing Trust, Robin Gandy, and P.N. Furbank. I am grateful to Donald Michie, Chairman of the A.M. Turing Trust, and to Peter Croft, Librarian of King’s College, Cambridge, for facilitating the granting of this permission. I am grateful also to the Headmaster of Sherborne School for permission to reproduce those records held at Sherborne.
Transcripts of Crown Copyright records in the Public Record Office appear by permission of the Controller of Her Majesty’s Stationery Office. So do the extracts from British Intelligence in the Second World War. I am grateful also for specific permission to reproduce photographs of the Colossus and the Delilah.
Private letters and papers are reproduced by permission of the many individuals who have kindly made them available.
I am grateful to the London Mathematical Society, and to Harvester Press, for permission to reproduce long extracts. The authors and publishers of other quotations are acknowledged in the Notes above.