The theme of The Hunchback of Notre Dame, by Victor Hugo, is difficult to narrow down to a single one, as there are many that intertwine throughout the narrative. Perhaps the greatest consistent theme throughout, however, is that of love, especially sacrificial love, and especially when everything else—social standards, cultural expectations, others' opinions, even perhaps your own prejudices and hesitations—seems to stand against love as completely irrational and/or ridiculous.

One of the clearest examples in Hunchback of an obstacle that some would consider insurmountable to true love is the physical appearance of the titular character, however shallow or unkind an obstacle that may seem. Quasimodo is consistently described as unsightly to behold. He therefore assumes himself to be unloveable, and certainly the townspeople and even Frollo consider him to be unloveable, as though Quasimodo's physical appearance is the only trait that matters.

And yet, throughout the novel, there are numerous instances of love, with varying degrees of genuineness and success: Esmeralda's love for Phoebus, Quasimodo's love for Esmeralda, Frollo's so-called "love" for Esmeralda, Quasimodo's "love" (of sorts) for Frollo, and so on. Indeed, perhaps the theme of the novel can be best summarized in a line that Victor Hugo gave to the story's narrator: "Love is like a tree: it grows by itself, roots itself deeply in our being and continues to flourish over a heart in ruin. The inexplicable fact is that the blinder it is, the more tenacious it is. It is never stronger than when it is completely unreasonable" (book IX, chapter IV).

The real theme of Victor Hugo's Notre-Dame de Paris, as The Hunchback of Notre Dame was originally entitled, was to bring attention to the beauty, grandeur, and history of Gothic architecture so that the Parisians would be made aware of the necessity of preserving this architecture.

However, as the narrative of Hugo's book is probably what is under consideration for this question, the theme for the narrative that is more closely connected to the plot than others while still paralleling Hugo's design for the preservation of gothic architecture is that goodness often appears in unsightly ways while evil manifests itself in unholy ways. Quasimodo, deformed of body but sensitive of soul, who resembles a gargoyle and is ridiculed by the Parisian crowd, is the truly saintly hero of the narrative while the bishop, Fra Claude Frollo in his obssession with alchemy and lust for gold as well as his licentious desire for Esmeralda, is truly evil.