ONB

ONB may refer to:
 * Old National Bank, an American regional bank
 * One Network Bank, a rural bank in Mindanao, Philippines
 * Opera Nazionale Balilla, an Italian Fascist youth organization
 * Order of New Brunswick, a Canadian decoration (post-nominal letters)
 * Orthonormal basis, a notion in linear algebra
 * Österreichische Nationalbibliothek, the national library of Austria

See further:
 * OeNB for Oesterreichische Nationalbank