The fictional world in C.S. Lewis’s seven-book Chronicles is Narnia.
Narnia is a fantasy world populated by talking animals, humans, dwarfs, giants, and other beings. Lewis created it for The Chronicles of Narnia, a sequence of seven books published between 1950 and 1956. The stories include recurring ideas about creation, courage, sacrifice, temptation, and restoration, while each book has its own plot and setting.
The series begins, in its publication order, with The Lion, the Witch and the Wardrobe. The later books explore Narnian history both before and after the events of that first-published story. The final volume, The Last Battle, depicts the end of Narnia and was published in 1956.
Narnia is often confused with Middle-earth, J.R.R. Tolkien’s fictional setting, or Earthsea, created by Ursula K. Le Guin. Those are separate literary worlds. Lewis also wrote science fiction set in a different fictional environment, so not every Lewis fantasy belongs to Narnia.