Joseph Andrews was written in response to Samuel Richardson's novel Pamela, published two years earlier under a pseudonym which led some to believe it was the work of Colley Cibber. (This explains the references to Cibber in the text.)
Warning: wikipedia contains spoilers
Fielding set out to parody Pamela, and his central character, Joseph Andrews, is supposedly Pamela's brother. The story is comic and ribald, beginning with the virtuous young Joseph being thrown out of his employment because of his refusal to be seduced by the lady of the house. A string of adventures follows, in the course of which Joseph is befriended by Parson Abraham Adams and finally discovers true love.