The books' inclusion in public and school libraries has been frequently challenged for their focus on magic, particularly in the United States, where it was ranked seventh on the list of the most challenged books in American libraries between 1990 and 2000 despite having been first published in the United States in 1998. In 1999, the "Harry Potter" books were challenged 23 times in 13 states. According to the American Library Association, they are now the most challenged books of the 21st century.