The relationship between NGOs and religion is of pivotal importance for understanding NGOs as such. Research that fails to attend to issues of religion neglects crucial features of NGO history and practice. While the recent ‘religious turn’ in development studies has helped rectify a historical neglect, this new literature has been dominated by instrumentalist frameworks and static conceptualisations of what ‘religion’ is and does. This chapter argues that historical and ethnographic methodologies can provide more nuanced understandings of the complex entanglements between NGOs and religion. Through textured and detailed analysis of particular cases, such approaches can facilitate greater attention to diversity and dynamism among ‘religious NGOs’ and ‘faith-based organisations’. We also argue for the use of these same methodologies to better understand how religious traditions are being reshaped by NGOs and their activities, as well as how secularity is experienced within ‘secular NGOs’.