The adventure novel is a genre of novels that has adventure, an exciting undertaking involving risk and physical danger, as its main theme. Adventure has been a common theme since the earliest days of written fiction.
Indeed, the standard plot of Medieval romances was a series of adventures. Following a plot framework as old as Heliodorus, and so durable as to be still alive in Hollywood movies, a hero would undergo a first set of adventures before he met his lady. A separation would follow, with a second set of adventures leading to a final reunion. Variations kept the genre alive.
From the mid 19th century onwards, when mass literacy grew, adventure became a popular subgenre of fiction. Examples of that period include Alexandre Dumas, père, Jules Verne, H. Rider Haggard, Emilio Salgari, Louis Henri Boussenard, Thomas Mayne Reid, Sax Rohmer, Edgar Wallace, John Ronald Reuel Tolkien and Robert Louis Stevenson.
Adventure novels often overlap with other genres, notably war novels, crime novels, sea stories, Robinsonades, science fiction, fantasy, and Westerns. Not all books within these genres are adventures. Adventure novels take the setting and premise of these other genres, but the fast-paced plot of an adventure focuses on the actions of the hero within the setting.