How many books in the dark tower series?

 Stephen King wrote the series of The Dark Towers. This series is composed of 8 books which are listed as follows:
The Dark Tower: The Gunslinger
The Dark Tower II: The Drawing of the Three
The Dark Tower III: The Waste Lands
The Dark Tower IV: Wizard and Glass
The Dark Tower: The Wind Through the Keyhole
The Dark Tower V: Wolves of the Calla
The Dark Tower VI: Song of Susannah
The Dark Tower VII: The Dark Tower

The first of these book was released in 1982 while the last one was released in 2004.
This series has multiple themes and genres including horror, dark fantasy and science fantasy.
The last one of the series "The Dark Tower VII: The Dark Tower" won the 2005 British Fantasy Award. Other books from the same series were also nominated to the Locus Award.