Human activities are creating environmental problems that affect everyone, and place all of us in a decision-making role about environmental issues. To make intelligent decisions, we need to understand how the environment works; therefore, each of the activities in this book was designed to teach one or more basic concepts of environmental science. Environmental issues generate strong opinions, extreme positions and contradictory claims. To analyze these issues requires not only understanding of the environment, but also an ability to evaluate evidence and arguments critically. Therefore, another major purpose of this book is to provide opportunities for readers to practice critical thinking and scientific methods of inquiry.