Cosmic

Out of the Silent Planet (1938)
Perelandra (1943) aka Voyage to Venus
That Hideous Strength (1945) aka The Tortured Planet
The Space Trilogy (omnibus) (1975)
The Cosmic Trilogy (omnibus) (1990)

Chronicles of Narnia

The Lion, the Witch and the Wardrobe (1950)
Prince Caspian (1951)
The Voyage of the Dawn Treader (1952)
The Silver Chair (1953)
The Horse and His Boy (1954)
The Magician's Nephew (1955)
The Last Battle (1956)
The Chronicles of Narnia (omnibus) (1976)
The Complete Chronicles of Narnia (omnibus) (1998)

Novels

A Pilgrim's Regress (1933)
Rehabilitations (1939)
The Screwtape Letters (1942)
The Abolition of Man (1943)
Beyond Personality (1944)
The Great Divorce (1945)
Vivisection (1948)
Till We Have Faces (1956)
The Discarded Image (1964)
Screwtape Proposes a Toast (1965)

Collections

Spirits in Bondage (1919) (writing as Clive Hamilton)
Dymer (poems) (1926) (writing as Clive Hamilton)
Miracles (1947)
The Four Loves (1960)
Poems (poems) (1964)
Letters to Malcom (1964)
Of Other Worlds (1966)
The Dark Tower: And Other Stories (1977)
Of This and Other Worlds (1982)
The Complete Poems (poems) (2004)

Non-fiction

Allegory of Love (1936)
The Personal Heresy (1939) (with E M W Tillyard)
The Problem of Pain (1940)
The Weight of Glory (1942)
Broadcast Talks (1942)
Mere Christianity (1952)
English Literature in the Sixteenth Century (1954)
Surprised by Joy (1955)
Reflections On the Psalms (1958)
Shall We Lose God in Outer Space? (1959)
A Grief Observed (1961) (writing as N W Clerk)
Studies in Medieval And Renaissance Literature (1966)
C.S. Lewis on Faith (1970)
The Inspirational Writings of C.S. Lewis: Surprised by Joy: Reflections on the Psalms; The Four Loves ;The Business of Heaven (1972)
The Riddle of Joy (1989) (with G.K. Chesterton)
Arthur C. Clarke and C.S. Lewis: A Correspondence (2001) (with Arthur C Clarke)
From Narnia to a Space Odyssey: The War of Letters Between Arthur C. Clarke and C.S. Lewis (2003) (with Arthur C Clarke)
A Year with C. S. Lewis: 365 Daily Readings from His Classic Works (2003) (with Patricia Klein)
The Collected Letters of C.S. Lewis, Volume 1: Family Letters 1905-1931 (2004)
The Collected Letters of C.S. Lewis, Volume 2: Books, Broadcasts and the War, 1931-1949 (2004)

Anthologies containing stories by C.S. Lewis

The Best from Fantasy and Science Fiction 6th Series (1957)
Fantasy Stories (1994)
The Book of Dragons (1995)
Fantasy Stories (1996)
The Science Fiction Century (1996)
The Wizards of Odd: Comic Tales of Fantasy (1996)
The Flying Sorcerers (1997)

Short stories

The Adventures of Eustace (1952)
The Dark Island [from The Voyage of the Dawn Treader] (1952)
Ministering Angels (1955)
The Shoddy Lands (1956)