Environmental impact assessment (EIA) is named explicitly in the GS Paper III syllabus. It is the main tool for deciding whether, and on what conditions, a mine, dam, highway or factory should go ahead — which makes it the meeting point of development and conservation.

What UPSC asks

Prelims: the legal basis of EIA in India; Category A and B projects and who appraises them; the four stages; the public hearing; Coastal Regulation Zone categories; strategic environmental assessment; international instruments such as the Espoo Convention.
Mains GS III: weaknesses of the EIA process, ex post facto clearances, the role of public participation, cumulative and strategic assessment, and reforms that balance ease of doing business with environmental safeguards.

Key sub-topics

Sub-topic	What to master
Concept and history	Purpose of EIA; NEPA (USA, 1969); India’s 1994 and 2006 notifications
Process	Screening, scoping, public consultation, appraisal; post-clearance monitoring
Institutions	MoEFCC and Expert Appraisal Committees; SEIAA and SEAC; pollution control boards; accredited consultants
Related clearances	Forest, wildlife and coastal (CRZ) clearances; the PARIVESH portal
Beyond project EIA	Strategic environmental assessment, cumulative impact assessment
Debates	Draft EIA Notification 2020; ex post facto clearance; quality of EIA reports

The parent law, the Environment (Protection) Act, 1986, is explained in Environmental Laws and Institutions.