This chapter provides an introduction to the concept of critical environmental justice, which builds on earlier foundations of environmental justice scholarship by moving the field in four key directions. This concept is then applied to the case of the US prison system to illustrate how environmental justice scholarship is useful for understanding spaces of state violence and grassroots resistance. The fact that US prisons are also sites of legal enslavement also opens up the possibility of rethinking the movement for environmental justice inside and outside of prisons as linked to centuries of slave revolts and to the broader movement for the abolition of slavery.