Freedom of opinion is a fundamental human right and one of the most valuable assets of liberal societies. As such, it is greatly feared by authoritarian systems. 90 years ago, the National Socialists burnt books at more than 160 sites throughout Germany in the hope of silencing opinions, world views and authors whom they considered undesirable. Even today, freedom of opinion cannot be taken for granted. There are many places in the world in which people are prevented from expressing their opinions freely, where they are imprisoned, expelled, their books censored and banned. As in earlier times, suppression has driven many of those affected into exile.