Sustainability is a term with an evolving definition that applies to more than the physical environment. It speaks to the interconnectivity of every action we take (or fail to take) and to human beings' relationships with one another and their environment. A sustainable future is one in which global citizens engage in critical thinking, problem-solving, and collaboration to create a just and equitable society for all. Teachers have a role in cultivating these critical competencies--and the knowledge to go along with them--in their students. As the authors point out, this involves much more than a simple classroom recycling project or a field trip to the zoo. A broad conception of sustainability will foster students' ability to understand and live harmoniously in diverse societies. Through a holistic approach to sustainability, teachers can model for students how we can bring about a more peaceful and compassionate future.