Westpac Banking Corporation, more commonly known as Westpac, is an Australian bank and financial-services provider headquartered in Westpac Place, Sydney. It is one of Australia's "big four" banks. Its name is a portmanteau of "Western-Pacific".

As of November 2015, Westpac has 13.1 million customers, and is Australia's largest branch network, with 1429 branches and a network of 3850 ATMs. The bank is Australia's second-largest bank by assets. It is also the second-largest bank in New Zealand.