Unit 1 provides an introduction to environmental studies. It discusses the multidisciplinary nature of environmental studies, drawing on fields like zoology, botany, ecology, geology, chemistry, social sciences, philosophy and more. It examines the key components of the environment - the atmosphere, hydrosphere, lithosphere and biosphere. Finally, it discusses the concepts of sustainability and sustainable development, giving the Brundtland definition, and provides a brief history of environmentalism, highlighting international conferences and key Indian environmentalists.