An index expurgatorius is a list of prohibited books or publications. Synonyms for this term include a banned books registry, index librorum prohibitorum, and a forbidden literature index. The concept of censorship and book banning has a long history, with various governments and religious institutions taking steps to control and restrict access to certain ideas and texts. In the modern era, debates continue to rage over the morality and efficacy of such practices, with proponents arguing that censorship protects public morality and opponents arguing that it stifles free speech and intellectual inquiry. Regardless of one's views on the subject, the existence of an index expurgatorius remains a contentious issue in many societies.