In 1712 Isaac Newton sent a portrait of himself to Roger Cotes, who was then working with Newton as the editor of the second edition of Newton’s Principia. Cotes acknowledged the gift with thanks in a letter to Newton, but the identity of the portrait, presumed to be an engraving done from one of the original portraits in oil, is a mystery. There are only a few engraved portraits to consider as possibilities. Two of them have been suggested as the portrait that Newton sent to Cotes, but an examination of the dates of those engravings rules out that possibility. A third possibility exists as a unique print in the collection of the Wellcome Library, and it now seems a better, if not the only, candidate.