In the preface to Joseph Andrews, Fielding defines the conventions of what he calls the "comic epic poem in prose." This differs from other forms of comedy in terms of length, a " larger circle of incidents," and a "greater variety of characters," as serious epic differs from other forms of literature. It also departs from the conventions of serious romance by being "light and ridiculous," introducing characters from a wide spectrum of society, particularly those of inferior rank, and "by preserving the ludicrous instead of the sublime" in sentiment and diction. Fielding suggests that this was the pattern of a lost comic poem by Homer. However, in the absence of this ancient model, he is setting out the elements of the genre himself rather than following a pre-existing pattern.

It is, therefore, scarcely surprising that Joseph Andrews contains all the elements Fielding describes. First it is a long book and is epic in the number and variety of the adventures it describes. The characters are varied, and the hero is of low social rank, being a servant. The light, ridiculous comedy comes from the reversal of traditional gender roles in that it is the male protagonist who has to preserve his chastity in the face of attacks by Lady Booby and other predatory women. This is a comic reversal of the conventions employed by Samuel Richardson with the virtuous heroines of his novels.