This paper reports on the findings of a large scale study of the impact of anti-vilification (or ‘hate speech’) laws,1 on public discourse in Australia over more than two decades.2 Its scope includes, but is not limited to s 18C of the Racial Discrimination Act 1975 (Cth). We investigated the ways in which legislation might have affected public discourse over time. Our task was methodologically challenging, for connecting changes in public discourse to the introduction or enforcement of hate speech laws is fraught with difficulty. We triangulated data from a range of primary and secondary sources, to investigate the relationship between hate speech laws and public discourse over time. Sources include complaints data from, and interviews with, federal and state/territory human rights authorities; tribunal and court decisions; qualitative document analysis of letters to the editor published in newspapers; data from community organisations regarding their members’ experiences; and interviews conducted with members and representatives of target communities.