The contribution addresses the role of Muslim NGOs in environmental sustainability. Reviewing empirical studies about this topic, it discusses the potentials and challenges of Muslim NGOs to promote environmental sustainability. Crucial resources for this endeavour are the environmental teachings of Islam and the grassroots reach of these organisations. Religious scholars often stress the rich scriptural resources of Islam for tackling environmental issues. Moreover, unlike other (secular) NGOs, Muslim NGOs can reach local populations in Muslim majority countries where they usually enjoy high credibility. Existing studies mention numerous initiatives of Muslim NGOs to advance environmental sustainability, among them radio campaigns, tree-planting activities, environmental awareness and education programs, the dissemination of environmental knowledge through religious leaders, the issuing of fatwas to declare logging illegal, and the implementation of sustainable resource management in Muslim organisations. Nevertheless, there are also important challenges to this environmental engagement. The Islamic environmental ethics that environmentally concerned Islamic scholars and activists highlight reflect their own perceptions of Islam, but not necessarily that of the broader Muslim population. As such, at the grassroots level, there is often low acceptance for Islamic environmental initiatives that have, consequently, little impact. In total, while bearing specific potentials for reaching wider populations through its grass-roots reach, Muslim environmentalism remains often limited to the environmental concerned Muslim organisations and activists.