What are the themes of The Da Vinci Code?

If by themes you mean both the themes and ideas behind the movie, one could say that one rather obvious theme is that of a historical mystery as they search for hidden clues, hidden by secret cults. There is also a sense of adventure, almost like a pirate treasure hunt, to find history's gold! To sum up, the main and minor themes of the Da Vinci Code are murder mystery and adventure.

However, if one means the themes of the book itself, these would be of Leonardo Da Vinci, the Priory of Sion and Opus Dei, two secret cults and organisations, both with strong beliefs and rituals.