To help Member States' authorities and developers manage the environmental consequences of construction projects more easily, the European Commission has brought together all existing EU legislation governing environmental impact assessments. The original Environmental Impact Assessment (EIA) Directive and its three subsequent revisions have been combined to create a more compact, clearly translated and user-friendly version.

The aim of the EIA Directive is to ensure that projects which are likely to have a significant effect on the environment are adequately assessed before they are approved. Hence, before any decision is taken to allow such a project to proceed, its possible impacts on the environment are identified and assessed. Developers can then adjust projects to minimise negative impacts before they actually occur, or the competent authorities can incorporate mitigation measures into the project approval.
This "codification" is part of an ongoing effort to simplify the EU's regulatory environment. It means that the EIA Directive and all its subsequent amendments now form one single transparent and readable piece of legislation, without any change to its original provisions.

More information: http://ec.europa.eu/environment/eia/eia-legalcontext.htm