Fielding melds elements of several traditional literary forms in Tom Jones. First, the novel borrows some elements of epic poems, such as Homer's Odyssey. In fact, in the novel itself, Fielding, as narrator, calls the book a "prosaicomiepic," meaning a comic epic written in prose.
Second, Tom Jones incorporates elements of the picaresque novel, which originated in Spain. A picaresque features a roguish hero (picaro in Spanish) and is episodic and more loosely structured than an epic. A picaresque is literally "one thing after another," and the only unifying thread may be that all events befall the central character. Many picaresques center on a journey, and most satirize the society in which the story takes place.Tom is certainly a roguish character, and Tom Jones certainly satirizes the society in which he moves.
Finally, Tom Jones, to a lesser extent, borrows the form of the epistolary novel, or novel of letters and utilizes many opportunities to advance his story through letters written by his characters, who are often separated by geography, intrigue, or both.