Each year, the ALA's Office for Intellectual Freedom compiles a list of books that were most frequently challenged that year, as part of an informational campaign against censorship. Banned Books Week is an ALA tradition occurring in the last week of each September that spotlights these and other "banned" books, and the history of censorship in U.S. public schools and libraries. These were the most frequently challenged books in 2019, according to OIF data.