As in the Federal Reserve System, each Eurosystem policymaker is expected to act in the interest of the entire currency area. In the United States, once policy implementation boiled down to managing the consolidated balance sheet of the Federal Reserve Banks, it made sense to concentrate open market operations in New York, where most major banks and dealers had offices.
New York bought and sold on the FOMC’s orders, but the resulting portfolio was allocated to each Reserve Bank based on its capital. In the Eurosystem, open market operations are conducted in a unified but decentralized manner. Each national central bank collects bids from financial entities in its country and relays those to the ECB where they are ranked and allocated accordingly.