The Newton Letter is a novel by John Banville, first published in 1982. It was published in the United States in 1987. Drawing comparisons with Ford Madox Ford's The Good Soldier and John Hawkes's The Blood Oranges for their use of the unreliable narrator, The Newton Letter was described there as Banville's "most impressive work to date".
The book opens with: "Words fail me." It follows the adventures of an aspiring biographer of Isaac Newton who rents a rural retreat in the south of Ireland. He becomes involved with two women: Charlotte and Ottilie. Charlotte's husband, Edward, also appears. It has been observed that Charlotte, Ottilie and Edward are the three main characters of Goethe's 1809 novel Elective Affinities.
The Newton Letter is the third of Banville's "scientific tetralogy" and the writer has recommended those who wish to sample his work to begin with it, saying: "It's pretty well all there. And it's short."