The urge to censor is as old as the urge to speak. From the first Chinese emperor's wholesale elimination of books to the Vatican's suppression of pornography, right up to the attack on Charlie Hebdo and the advent of Internet troll armies in this century, words, images and ideas have always been hunted down by those trying to suppress them. In this compelling account, Eric Berkowitz reveals why and how humanity has, from the beginning, sought to silence itself. Ranging from the absurd - such as Henry VIII's decree of death for anyone who 'imagined' his demise - to claims by American slave owners that abolitionist literature should be supressed because it hurt their feelings, Berkowitz takes the reader on an unruly ride through history, highlighting the use of censorship to reinforce class, race and gender privilege, and to guard against offence. Elucidating phrases like 'fake news' and 'hate speech', Dangerous Ideas exposes the dangers of erasing history, how censorship has shaped our modern society and what forms it is taking today - and to what disturbing effects.