The themes of Eugénie Grandet are miserliness, frugality, avarice, and naivete. Old man Grandet has taken his business acumen to an extreme. He is shrewd enough to have extracted advantage from practically every transaction he has engaged in, which, combined with a fortunate series of inheritances and his extreme frugality, has left him the richest man in Saumer on the Loire. His daughter Eugénie knows little of the world and, as Grandet's sole heir, is the target of many suitors.

Balzac comments on how the loss of the aristocratic culture of honor, tempered by religion, that used to check the dominance of the narrow monetary values of the French bourgeoisie has been swept away by the revolution, leaving only the pursuit of money: "Misers hold no belief in a life beyond the grave, the present is all in all to them. This thought throws a pitilessly clear light upon the irreligious times in which we live, for today more than in any previous era money is the force behind the law, politically and socially. Books and institutions, the actions of men and their doctrines, all combine to undermine the belief in a future life upon which the fabric of society has been built for eighteen hundred years."

Sheltered Eugénie in her shabby clothes falls for her dashing young cousin from Paris, unaware of his father's impending bankruptcy. Only Grandet's banker and lawyer realize the extent of Grandet's fortune and send their own sons in pursuit of Eugénie's hand, but she has chosen to wait for the return of her cousin. When Eugénie's cousin returns from abroad having done well in trade, he spurns her in the mistaken belief that she is less well off (the Grandet family makes no display of its wealth). Instead, he marries an impoverished aristocrat leaving Eugénie heartbroken but wiser. In the end, Eugénie inherits and enjoys life by steering clear of the grasping and conniving types she has now learned about. She never overcomes the naive "feminine piety" of her sheltered upbringing and this leaves her not fully engaged in the world and she prefers the honest friendship of the lower classes.