Null-A Three, usually written Ā Three, is a 1985 science fiction novel by Canadian-American writer A. E. van Vogt.

One of the spare bodies used in his reincarnation machinery was found and forced to life by the approach of an immense space fleet from another galaxy, crewed by the primordial ancestors of humans, gripped in an eon-long war with mutants equally old.

The space-fleet is ruled by an unstable youngster who seems to possess many of the same powers as Gosseyn, including a double-brain.

Gosseyn must school the youth in Null-A sanity, save the Earth from a cabal of gangsters and businessmen who oppose the return of the Games Machine, discover the secret reasons behind the endless horrifying war, and stop the intrigues of Enro the Red to return to power.

Dave Langford reviewed Null-A Three for White Dwarf #64, and stated that "The book can only be read as parody or in a spirit (several bottles' worth) of overwhelming nostalgia for the 'Golden Age'.