Why is there so much hate on social media? How dangerous is online vitriol for politics and society? Can there be a universal definition of hate speech? International Journal of Communication publishes a special section on online extreme speech edited by ONLINERPOL project PI Sahana Udupa and SOAS researcher Matti Pohjonen. Contributions by Carole Mcgranahan, Peter Hervik, Iginio Gagliardone, Nell Haynes, Alexandra Deem, Ronan Lee and Omar Al-Ghazzi. Open access articles. Download them here or academia.edu.