National Australia Bank (abbreviated NAB, branded nab) is one of the four largest financial institutions in Australia in terms of market capitalisation and customers. NAB is ranked 17th largest bank in the world measured by market capitalisation. It operates across 10 countries serving 8.3 million consumer and business banking customers and over 2.3 million wealth management customers.

NAB operates 1,808 branches and service centres and 4654 ATMs globally. NAB has a "AA-" long term issuer rating by S&P.

The National Australia Bank Group is organised into nine divisions, spread across four geographic regions.

In 1893, National Bank Limited was formed. Up until 1 October 1981 it continued to trade as The National Bank of Australasia Limited, only after the merger with the Commercial Banking Company of Sydney Limited did it become known as National Australia Bank.

In 1858 Alexander Gibb, a Melbourne gentleman, enlisted Andrew Cruickshank, a local merchant and pastoralist, to raise the capital to establish National Bank of Australasia with headquarters in Melbourne. Cruickshank became its first chairman while Gibbs left after being passed over for the position of General Manager. The bank opened its first branch in South Australia the same year.