The fantasy world in C.S. Lewis’s seven-book series is called Narnia.
The Chronicles of Narnia follows children and other characters who enter, live in, or defend the land of Narnia. The world contains talking animals, fauns, dwarfs, giants, witches, kings, and other fantastic beings. Its history begins with creation in The Magician’s Nephew and concludes with the end of the world in The Last Battle.
The series was published between 1950 and 1956. Although the books can be read in publication order, some editions arrange them according to the internal chronology of Narnian history. That difference has led to occasional confusion about which book should be read first.
Narnia is not the same setting as Middle-earth, which was created by J.R.R. Tolkien, or Earthsea, which was created by Ursula K. Le Guin. Those worlds belong to different fantasy traditions and authors.