Compensatory measures may be required in the case of:

1. a. International legislation: the EU Birds Directive (1979) and the EU Habitats Directive (1992)
   b. National legislation on compensation

Underlying principles when compensation is required by international or national legislation:

• Species and habitats protected under (inter)national regulations require stringent constraints within the planning process and it is usually difficult to justify the social necessity for developments in protected areas, or areas with protected species.
• Financial compensation or compensation in terms of other values than the impacted ones (trading-off) should not be permitted.
• Ecological compensation must address physical and functional aspects of the impact.
• According to the Birds and Habitats Directives compensatory measures should be implemented before the start of the infrastructure development.

2. Formal compensation policy: nonlegislative regulation, e.g. laid down in national policy plans.

Where compensation is linked to formal national policy usually less stringent measures are required:

• Economic or social necessity may, in exceptional cases, justify project development, under the condition that ecological damage is compensated for.
• Compensation in terms of 'comparable' ecological values as well as financial compensation are both permitted, though less preferable.
• Compensatory measures do not necessarily have to be implemented before the project starts.

3. Compensation based on voluntary agreements, implying that it has neither a legislative nor a policy basis.

Non-legislative policy requires less stringent conditions on the implementation of the compensation principle. In the assessment process, socio-economic and nature conservation interests are weighed against each other.