In the tradition of grassroots environmental movements worldwide, activist Buddhist monks in rural Thailand have, since the late 1980s, led a popular movement to protect local forest, water and land resources while at the same time challenging dominant state and corporate "economist" development paradigms. Most famously, these "development monks" ("phra nak phathanaa") and "ecology monks" ("phra nak anuraksaa") have led local villagers and NGO activists in the symbolic ordaining of large trees and forests ("buat paa"). They do this in the hope that they will not only protect forests from logging, but also teach local people the value of conserving forest resources. This paper charts the history, philosophy and practice of the activist forest monk movement in Thailand, its contribution to our collective knowledge of adult education in new social movements, and its value to environmental adult education. (Contains 3 notes.)