Angels & Demons is a 2000 best selling mystery-thriller novel written by American author Dan Brown and published by Pocket Books. The novel introduces the character Robert Langdon, who is also the protagonist of Brown's subsequent 2003 novel, The Da Vinci Code; his 2009 novel, The Lost Symbol; and the 2013 novel Inferno. Angels and Demons shares many stylistic literary elements with its sequel, such as conspiracies of secret societies, a single-day time frame, and the Catholic Church. Ancient history, architecture, and symbolism are also heavily referenced throughout the book.