The Graveyard Book is not defined by any one genre; instead, the novel is a combination of the horror, paranormal fantasy, and Gothic genres, depicting a Bildungsroman storyline.
The story centers on the fate of one Nobody (Bod) Owens, whose family are all murdered by a member of the Jacks Of All Trades, a secret fraternity intent upon destroying all the members of Bod's biological family. Apparently, prophecy has it that Bod will eventually grow up to be the one responsible for the annihilation of the entire secret society.
Bod's protectors are the dead, who inhabit the graveyard at the top of a hill in Old Town. The Owens (his adopted parents), Silas (his guardian, strongly implied to be a vampire of sorts), and Miss Lupescu (a Hound of God who is a powerful were-wolf) are his main teachers. The story is filled with ghouls, night-gaunts (flying creatures), and ghosts of the dead. There is a gory scene (albeit done in good taste) at the beginning of Chapter 1, when Bod's family are murdered. This is the horror element.
The fantasy element comes in the form of special skills Bod learns as he matures. For example, he learns to disappear, using the Slip and Fade skill. He learns the rudiments of DreamWalking, where he can influence and control the direction of anyone's dreams. Using the Haunt skill, he can terrify or make anyone feel uneasy. From Miss Lupescu, Bod learns how to call for help in any language, from the language of the dead to the living. In the story, Miss Lupescu can transform from a human being to a hound. This dark fantasy story, complete with vampires, ghosts, and were-wolves, has its elements in 19th Century Gothic fiction.
From the book, we learn that Hounds of God are defenders of justice and goodness. Gothic fiction always involves dark and mysterious settings, whether it be lonely castles or, in this case, a graveyard. It also includes elements of the supernatural, dark omens, and prophecies.
Those that men call Werewolves or Lycanthropes call themselves the Hounds of God, as they claim their transformation is a gift from their creator, and they repay the gift with their tenacity, for they will pursue an evildoer to the very gates of Hell.
The Bildungsroman element presents itself in the form of Bod's emotional and mental progress throughout the novel; as he matures, he eventually comes to understand that he can't stay in the graveyard forever. By the time he is fifteen, he starts to lose his ability to see his ghostly friends and family. It is a bittersweet moment when he bids goodbye to his adopted mother and father. Yet, Bod goes out into the world well-equipped with every knowledge his dead friends and family have given him. At the end of the novel, he stands at the precipice of a grand adventure which both awaits and beckons him. He will be able to make his own choices and choose his own life. It is a fitting conclusion to this unique coming of age story.