The Amsterdam Treaty has created a new instrument for European integration: Closer Co-operation. This allows a majority of Member States, i.e. currently eight countries, to take joint action and use the institutions and procedures of the European Union for this purpose, thereby further developing European integration in a flexible way. This right is tied to several conditions that largely ensure that Closer Co-operation will not significantly affect the homogeneity of the legal area and will not lead to a sustained split of the Union. The following concise analysis is based on the more detailed study "Verstärkte Zusammenarbeit im Umweltbereich Möglichkeiten der Anwendung der in Titel VII TEU festgelegten Bestimmungen für Flexibilität im Umweltbereich" commissioned by the Austrian Federal Ministry of Environment, Youth and Family Affairs. It examines the legal requirements and political framework conditions which are necessary for applying the new procedure of Closer Co-operation to the Community's environmental policy. Furthermore, an analysis was performed to see in how far Closer Co-operation could generate a new dynamism in the development of European environmental policy and which long-term effects are to be expected on the integration process. The prerequisites laid down in the Treaty for the implementation of Closer Co-operation require further interpretation in some cases, but this does not preclude the instrument's practical applicability in European environmental policy.