The Birds and Habitats Directives are the cornerstones of EU nature conservation law, aiming at the conservation of the Natura 2000 network, a network of protected sites under these directives, and the protection of species. The protection regime for these sites and species is not absolute: Member States may, under certain conditions, allow plans or projects that can have an adverse impact on nature. In this case compensatory measures can play an important role in safeguarding the Natura 2000 network and ensuring the survival of the protected species. This contribution analyses whether taking compensatory measures is always obligatory, and discusses the aim and the characteristics of compensatory measures, in relation to other kinds of measures such as mitigation measures, usual nature conservation measures, and former nature development measures, and to the assessment of the adverse impact caused by the plan or project and of the alternative solutions. The questions will be discussed in light of the contents of the legislation, the guidance and practice by the European Commission, (legal) doctrine and case law, mainly of the Court of Justice of the European Union.