This book combines simple math, the metric system, and critical thinking to gain insight into relevant local, regional, and global environmental issues, with a focus on sustainability. The presentation of real-world issues and examples fosters the development of the math and analytical skills necessary to truly think critically and to understand these complex issues.   A seven-part organization examines basic concepts and tools, as well as topical, relevant, and timely issues related to principles of sustainability, population and migration, climate change, energy, consumption and the quality of life, threats to ecosystems, and sustainability and the individual.  For individuals interested in environmental studies and science, and in the relationship of math and science to the environment.