This thesis is a study of social criticism in the works of Leopoldo Alas ("Clarín"), a nineteenth century Spanish novelist, literary critic and short story writer. In Clarín's two major novels, "La Regenta" and "Su único hijo," and in his numerous short stories there is frequent criticism of the abuses of the clergy, the state of Spanish morality, the misunderstanding and misapplication of religion by the laity, the quality of education, literature, theater and medicine, the corruption of law and government and the treatment to which the poor and uneducated were subjected. Because of Clarín's techniques it can be said that he was the leader of the naturalistic movement in Spain. It can also be said that Clarín as a naturalist did not follow the tenets of the French school.