This chapter examines the theory of the ‘environmentalism of the poor’ proposed by Catalan ecological economist Joan Martinez-Alier and Indian historian Ramachandra Guha. The authors identify two types of environmentalism: one ideological and based on values, found in countries of the global North, and the other materialistic and based on interests, found in the poor countries of the global South. The chapter also offers a critical analysis of the concept of ‘environmental conflict’, a key element in the theory of the environmentalism of the poor, and finally an assessment of the relationship between the environmentalism of the poor, environmental conflict and the broad concept of ‘environmental justice’.