This briefing seeks to restart research and discussion around the roles of websites in contemporary online extremism and terrorism. The briefing opens by locating extremist and terrorist websites within an ecosystem framework. It follows-up by grappling with the question of what constitutes a ‘terrorist website’ and lays out a three-part categorisation that accounts for terrorist-operated websites, supporter sites, and ideologically adjacent sites. This section includes description and discussion of eight websites from across the ideological spectrum chosen for analysis herein. These websites were the official sites of Hamas, the PKK, and the Taliban; three IS supporter sites, namely Elokab, I3lam, and Shine of Islam; and two ideologically adjacent sites: the Nordic Resistance Movement’s official English language site and Daily Stormer. The next section reviews the academic literature on extremist and terrorist sites. The Analysis section, which takes-up the bulk of the report, addresses the content, purposes, and reach of our selected eight websites. Also discussed in this section is the refusal of hosting or other crucial services, such as DDoS protection, by website providers, which has led to the disappearance—sometimes for a short period, sometimes more permanently—of some extremist and terrorist sites from the Web. In the Conclusion, we sum-up our findings and point to the need for more research on the role of websites in contemporary extremist and terrorist online ecosystems and some of the directions this new work could take.