“On 25 May 2011, the President of the United States, Barack Obama, speaking to the parliament of the United Kingdom, singled out Newton, Darwin and Alan Turing as British contributors to science. Celebrity is an imperfect measure of significance, and politicians do not confer scientific status, but Obama’s choice signalled that public recognition of Alan Turing had attained a level very much higher than in 1983, when this book first appeared.”