The external environment of large advocacy organisations can be conceptualised as a ‘knowledge market’. This brings attention to symbiotic relations between the producers and consumers of advocacy-oriented knowledge. Looking at the cases of Amnesty International, Human Rights Watch and the International Crisis Group, this chapter traces the history of these NGOs’ respective knowledge markets from their formation through to the present day. It is observed that evolving constellations of consumers and producers create supply and demand pressures that shape the development of epistemic practices. Over time, these international NGOs have had to overcome specific legitimacy dilemmas in order to maintain their organisational prestige. With intensified globalisation, they have been exposed to a growing pressure to appease a multiplicity of consumers. Similarly, with the advent of the internet and social media, they have had to deal with the saturation of their knowledge markets with a cacophony of rival producers. These legitimacy dilemmas have affected both the scope and orientation of leading humanist advocates’ epistemic practices, incentivising a more commercial mode of knowledge production.