These days, the word "green," and the more comprehensive term "sustainability," surface in numerous arenas, whether it be exhortations to recycle more, employ compact fluorescent lightbulbs, use less hot water, avoid products with excess packaging, adjust thermostats, plant trees, turn off electronic devices when not in use, or buy organic and local food. This article discusses what Montessorians are doing at an even deeper and more fundamental level to cultivate sustainability. Montessori students not only read and write and compute, they have a broad knowledge base upon which to become lifelong learners who respect self, others, and the environment. Ecological sustainability principles and authentic Montessori practices present new paradigms for living in this world, stimulating critical and creative thinking through content and process. Ecological sustainability and Montessori principles follow approaches that are holistic and systems oriented, attuned to living in harmony with the earth. They share a vision that recognizes humans as living beings and part of nature, comprising one web on one planet in a vast universe of profound mystery. Ultimately, both present a way of living--and establish a necessary, new way of thinking.