"Sustainable Development" (SO) has become part of the primary legislation in 1997: it is a task and aim of the EU (acc. to Preamble Recital 8 EU, Art. 2 EU, Art. 2 EC and Art. 6 EC). Still there is no comprehensive understanding of how to interpret these provisions and how to weigh the aim SO facing competing aims like "high level of employment and of social protection" in Art. 2 EC. It also requires an adjustment of the interpretation of secondary legislation, where a weighing of environmental and other public interests occurs, e.g. in the Habitat-Directive. Recently SO was also explicitly introduced in the secondary legislation. Art. 4 (3) and (7) WFD refer to: " ... sustainable human development activity ... " to justify non-compliance with environmental objectives calling for a case-by-case interpretation of SO with respect to individual projects.