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