Letters to Malcolm: Chiefly on Prayer was published posthumously in 1964 as letters to an imaginary friend.
Letters to Malcolm: Chiefly on Prayer presents a sequence of informal, fictional letters in which Lewis discusses prayer, worship, church practice, suffering, and Christian belief. The named recipient, Malcolm, is not a conventional biographical correspondent; the format allows Lewis to explore ideas conversationally while addressing a thoughtful imagined reader.
Lewis died in November 1963, and the book appeared after his death in 1964. It therefore differs from collections assembled from his actual correspondence. The work is also distinct from The Screwtape Letters, which uses letters from a senior demon, and from A Grief Observed, which focuses on personal bereavement. Its central subject is the practice and meaning of prayer.