The Eurosystem consists of the ECB and the national central banks (NCBs) of those EU countries that have adopted the euro. Under Article 8 of the Statute of the European System of Central Banks (ESCB Statute), it is the ECB's decision-making bodies that govern the Eurosystem. Within their respective responsibilities, these bodies take all the decisions that are necessary to enable the Eurosystem to carry out its tasks.
Except for the statutory tasks that have been exclusively assigned to the ECB, the ESCB Statute does not indicate to what extent ECB policies are to be implemented through activities of the ECB or the NCBs. For the bulk of the Eurosystem's activities, the actual intra-System division of labour has been guided by the principle of decentralisation, with the ECB having recourse to the NCBs, to the extent deemed possible and appropriate, to carry out operations which form part of the tasks of the Eurosystem (cf. Article 12.1 of the ESCB Statute).
Thus, the ECB and the NCBs jointly contribute to attaining the Eurosystem's common goals. However, according to Article 9.2 of the Statute, the ECB has to ensure that all tasks are carried out properly and consistently. To ensure this across the euro area, the ECB has the power to issue guidelines and instructions to the NCBs.
OR.011 01/12European Central Bank