An Environmental Impact Declaration (DIA) is an official document in which the result of an environmental impact assessment and its allegations are recorded. It is a mandatory document for the construction of a large number of infrastructures in some countries, such as roads. For example, in all EU Member States through Directive 85/337/EEC and its successive transpositions and amendments, such as Directives 2001/42/EC, 2011/92/EU and 2014/52/EU.

The document is prepared by the competent environmental authority of the affected area, such as a Ministry of the Environment. Once the project is defined by its writers, it is sent to this authority, which must be independent of the interests of the project. The environmental impact assessment is drawn up and subjected to a period of public exposure, after which the allegations that have been made are assessed and the appropriate modifications are made.

The final document states whether the assessment is positive or negative, and if positive, what measures must be adopted to reduce the environmental impact of both the work and the infrastructure finally built.