The Da Vinci Code is a 2003 mystery-detective fiction novel written by an American author, Dan Brown. It follows symbologist Robert Langdon and Sophie Neveu as they investigate a murder in Paris's Louvre Museum and discover a battle between the Priory of Sion and Opus Dei over the possibility of Jesus Christ of Nazareth having been married to Mary Magdalene.

The title of the novel refers to, among other things, the fact that the murder victim is found in the Denon Wing of the Louvre, naked and posed like Leonardo da Vinci's famous drawing, the Vitruvian Man, with a cryptic message written beside his body and a pentacle drawn on his stomach in his own blood.

The novel has provoked a popular interest in speculation concerning the Holy Grail legend and Magdalene's role in the history of Christianity. The book has been extensively denounced by many Christian denominations as an attack on the Roman Catholic Church. It has also been criticized for its historical and scientific inaccuracy.

The book is a worldwide bestseller that sold 80 million copies as of 2009[update] and has been translated into 44 languages. This makes it, as of 2010, the best selling English language novel of the 21st century and the 2nd biggest selling novel of the 21st century in any language. Combining the detective, thriller, and conspiracy fiction genres, it is Brown's second novel to include the character Robert Langdon, the first being his 2000 novel Angels & Demons. In November 2004, Random House published a Special Illustrated Edition with 160 illustrations. In 2006, a film adaptation was released by Sony's Columbia Pictures.

This book describes the attempts of Robert Langdon, Professor of Religious Symbology at Harvard University, to solve the murder of renowned curator Jacques Saunière of the Louvre Museum in Paris. A baffling cipher is found near his body. Saunière's granddaughter, Sophie Neveu and Langdon attempt to sort out the bizarre riddles and are stunned to discover a trail of clues hidden in the works of Leonardo Da Vinci.

The unraveling of the mystery requires solutions to a series of brain-teasers, including anagrams and number puzzles. The ultimate solution is found to be intimately connected with the possible location of the Holy Grail and to a mysterious society called the Priory of Sion, as well as to the Knights Templar. The story also involves the Roman Catholic organization Opus Dei.

The story starts off with the murder of Jacques Saunière (the Grand Master Of Priory of Sion, although virtually no one knows that at the time) by Silas (acting on behalf of someone known only as The Teacher) to extract the location of the "keystone", an item that leads to the Holy Grail. The police summon Robert Langdon, who is delivering a lecture in Paris, to the murder scene and ask for his help in deciphering the code Sauniere left on and near his body. Bezu Fache, the Captain of the Central Directorate Judicial Police, believes Langdon is the prime suspect in the murder.

Sophie Neveu shows up at the murder scene as a police cryptographer and quickly gains Langdon's trust. Jacques Saunière was Neveu's grandfather and they were very close to each other until she discovered him participating in a pagan sex ritual (Hieros Gamos) at his home in Normandy, when she made a surprise visit there during a break from boarding school. (That she had observed something is mentioned and hinted at several times throughout the story, but what it is that she saw is revealed to no one, including the reader, until near the end when she tells Robert).

Langdon and Neveu find a baffling cipher near Saunière's body. These clues were meant to lead to a second set of clues. By deciphering her grandfather's clues, Neveu finds the painting, which has a key hidden behind it with an address and symbols of the Priory of Sion were written on it. Working together, Langdon and Neveu trick the police, flee the scene and figure out the secret of the key.

The key opens a safe deposit box at the Paris branch of the Depository Bank of Zurich. Saunière's account number at the bank is a 10-digit number listing the digits of the first eight Fibonacci numbers: 1 1 2 3 5 8 13 21.