National Australia Bank Limited (abbreviated NAB, branded and stylised as nab) is one of the four largest financial institutions in Australia (colloquially referred to as "The Big Four") in terms of market capitalisation, earnings and customers. NAB was ranked the world's 21st-largest bank measured by market capitalisation and 52nd-largest bank in the world as measured by total assets in 2019.

As of January 2019, NAB operated 3,500 Bank@Post locations—including 7,000+ ATMs across Australia, New Zealand, and Asia—and served 9 million customers.

NAB has an "AA−" long-term issuer rating by Standard & Poor's.