Ion Courtenay Gill Trewin (13 July 1943 - 8 April 2015) was a British editor, publisher and author.
Trewin was educated at Highgate School. He was the literary editor of The Times from 1972-1979 and then with Hodder & Stoughton (for whom he published Thomas Keneally's Schindler's Ark) until 1992 and Orion Publishing Group to 2006. He was said to have 'an unmatched reputation as a publisher of taste and acumen'.
- Alastair Niven. "Ion Trewin obituary". the Guardian. Retrieved 13 April 2015.
- "Ion Trewin: Guiding hand behind lauded big-name biographies who became the literary director of the Man Booker prizes". The Independent. Retrieved 13 April 2015.
- "Obituary: Ion Trewin, author and publisher". scotsman.com. Retrieved 13 April 2015.
- "Death of Ion Trewin". thebookseller.com. Retrieved 13 April 2015.
- "Man Booker Prize director Ion Trewin dies at 71". BBC News. Retrieved 13 April 2015.