What is the title of C.S. Lewis’s final published book?

C.S. Lewis’s final published book was Letters to Malcolm: Chiefly on Prayer.

Letters to Malcolm: Chiefly on Prayer was published posthumously in 1964, after Lewis died in 1963. Written in the form of letters to an imagined correspondent named Malcolm, the book considers prayer, worship, church practice, and Christian life. It was the last of Lewis’s books to appear in print during the immediate period after his death.

The work is sometimes confused with A Grief Observed, which Lewis published in 1961 under the pseudonym N.W. Clerk. That book is a direct and emotionally raw response to the death of his wife, Joy Davidman. Letters to Malcolm instead uses an epistolary structure to examine prayer and related theological questions.

The Last Battle is also an easy source of confusion because it was the final Narnia novel, not Lewis’s final published book overall. Distinguishing “final Narnia book” from “final published book” yields different answers.