Early on in his career as a mega-successful novelist, Stephen King got bored of constantly answering the question, "Why do you write horror stories?" and so he used his lectures on the subject of Gothic literature at the University of Maine to draw up a non-fiction book about the horror genre. The resulting work - Danse Macabre - covered horror fiction in print, radio, film and comics, and the genre's influence on U.S. popular culture in the period from 1950 to 1980. The book came out in 1982, and immediately caught the attention of the public, first by shining some light on King's personal attachment to horror comics and films in his youth - all told in the casual style typical for his fiction - and then by exploring common archetypes such as the Vampire-Werewolf-Thing trinity, and the Apollonian-Dionysian nature of horror. The book serves particularly well as a document of American radio programs, B-movies and TV productions made during the period covered, although King does get a bit stuck in the mud on few occasions such as the original Kolchak: The Night Stalker TV series of which he is very critical.
All in all, Danse Macabre is the best starting point for anybody who has passed the stage of mere curiosity about the genre and has acquired proper interest for scary movies and books. Given King's masterful storytelling, I'd even say that anybody with taste for non-fiction would enjoy this book for what it is. Simply put, Danse Macabre is one of the most important books ever published on the horror genre, along with H.P. Lovecraft's own Supernatural Horror in Literature (1927) and Carol J. Clover's Men, Women, and Chainsaws: Gender in the Modern Horror Film (1992).
Download Danse Macabre, and have fun while reading it, or go on and buy it - it's a book worth reading a couple of times.