This brief views the environment through diverse lenses – those of standard economics, institutional economics, political science, environmental science and ecology. Chapter 2 discusses diverse theoretical and statistical models – constrained optimization models, game theory, differential equations, and statistical models for causal inference – in a simple manner. Developing countries have certain distinct environmental problems – traditional pollution and traditional dependence on the commons. While chapters 3 and 4 discuss these specific problems, statistical graphs of the World Development Indicators explore the macro-context of developing countries in chapter 1. Chapter 5 examines ecological systems, which are nonlinear and unpredictable, and subject to sudden regime shifts. Chapter 6 deals with the global challenges of climate change and biological invasions. The last chapter discusses sustainable development and institutions. The brief explains these topics simply; mathematics is largely confined to an appendix. The broad treatment and simple exposition will appeal to students new to the field of economics. The extension of core economic models in diverse directions will also be of interest to economists looking for a different treatment of the subject.