The need for a cumulative impact assessment is laid down in the EIA Directive (97/11/EEC) and in the Habitats Directive (92/43/EEC) and requires that the impacts of a project be assessed ‘cumulatively’, or ‘in combination’ with other projects. 

The objective of the CIA is to determine the affects on the environment of the project when taken into consideration with additional projects that are either being developed or planned. 

The CIA process is similar to the EIA process and includes: scoping to identify key issues and likely impacts; analysis of the effects following the collation of baseline data; identification of mitigation; and evaluation of the significance of the residual effects.