In December 2009, political attention was turned towards the 15th UN Climate Conference, COP15. For the Global Justice Movement (GJM) this provided an opportunity to promote their agenda. The use of online media conjured up memories of the success of alternative media in mobilising large-scale protests around previous WTO and G8 counter-summits. However, the COP15 saw a turn to the use of what can be termed mainstream – online sites among activists. Drawing on a case study of the activist network NTAC, the paper explores how YouTube served both the purpose of reaching broader publics and of mobilising for confrontational direct action within activist circles.