Federal Reserve bank notes, also called "national currency," are currency of individual banks in the Federal Reserve system. Meanwhile, Federal Reserve notes were issued by the system itself, and the obligation to pay the bearers of those notes went back to the United States government.
Two separate issues of the Federal Reserve bank notes were made, with the Series of 1915 consisting of $5, $10, and $20 notes issued by the banks of Atlanta, Chicago, Kansas City, Dallas, and San Francisco. The Series of 1918 included all denominations from $1 to $50 and were issued by all twelve banks, though not all banks issued all denominations.
Federal Reserve bank notes are considerably scarce. According to a government estimate, of the total issue of nearly $762 million, only $2 million remains outstanding.