The Natura 2000 appropriate assessment for impacting projects or plans under Article 6(3) HD is the central statutory instrument for the protection of Sites of Community Importance (SCI) and the Special Protection Areas (SPA). The decisive factor in whether or not an appropriate assessment is required depends on the question of whether a project or plan is present within the meaning of Article 6(3) of the Habitats Directive 92/43/EEC1 (HD). The Habitats Directive does not define these terms in any more detail, which is why they must be specified more closely through interpretation. This paper will present the definitions given by the European Court of Justice (ECJ)2 case law and national courts like the German Federal Administrative Court (BVerwG)3 and discuss the consequences and practical scope of the terms. The focus of the following investigation will be on the term “project”. This is because for “plans”, the envisaged projects are essentially also decisive, given that only these can have significant adverse effects on the conservation objectives. There are a variety of questions regarding when a human activity constitutes a project and under which conditions Member States could exempt activities from the requirement for an assessment. This article will start with an outline of the temporal scope of the appropriate assessment and, following this, briefly explore the scope of plans or projects directly connected with or necessary to the management of the site, as they are not the subject of an assessment.