Books written by prominent Hong Kong democracy activists have disappeared from the city's libraries, following the imposition of a new national security law by Beijing. The law targets acts of subversion, secession, terrorism, and colluding with foreign forces, and has raised concerns about academic freedom and censorship. The removal of the books is seen as a form of political persecution, with some authors believing it is a result of the new security law. The city's cultural services department has stated that the books are being reviewed to determine if they violate the national security law.