The updated second edition of the book offers an innovative synthesis of fundamental ecological concepts and practical applications in environmental science and conservation. It is the first textbook on the subject by eminent Indian researchers and presents most of the examples from the Indian subcontinent. The book covers a wide range of topics, including fundamental concepts required to comprehend the physical environment, population dynamics, community characteristics, patterns and gradients in biodiversity, ecosystem functioning and dynamics, and the study of biogeography. It also addresses applied topics such as environmental pollution, impact assessment, natural resource management, biodiversity conservation, ecosystem services, global climate change, ecosystem restoration, urban ecology and sustainable development. The main issues are discussed within the sustainability framework, considering humans as part of ecosystems, and recognising that sustainable development requires the integration of ecology with social sciences for policy formulation and implementation. The updated edition of the book aligns with the National Education Policy 2020 and the revised UGC Guidelines. It aims to meet the needs of students in basic and multidisciplinary courses in ecology and environmental science, as well as professionals in agriculture, forestry and geography at both the graduate and postgraduate levels.