Riverina is the largest of the four Big Rivers wine regions. Covering an area the size of Switzerland, this vast, almost perfectly square area of central-southern New South Wales produces correspondingly large quantities of wine. Riverina is a key workhorse of Australia's bulk wine production. Along with Murray Darling to the west, it produces almost three-quarters of New South Wales' entire annual wine output.

Although larger than Murray Darling, Riverina's vineyard density is lower. As a result, while Murray Darling produced more than 125,000 tons of Chardonnay in 2008, Riverina managed only 72,000 tons. However, that was enough to put Riverina at third place in the nation's Chardonnay-producing regions, behind South Australia's Riverland. Semillon is the second most-widely grown Riverina white variety and its plantings increased massively throughout the last decade. Despite this huge output of Chardonnay and Semillon, it is Shiraz which tops Riverina's production figures, accounting for 15% of Australia's Shiraz output.

The Lachlan and Murrumbidgee rivers which inspired Riverina's name flow from east to west across the region, en route from their sources in the Great Dividing Range to their convergence just beyond Riverina's western edge. The combined flow then continues south-west for some distance before joining the Murray and continuing westwards to meet the Darling outside Mildura, 100 miles (160km) downstream. The importance of these rivers is hard to overstate in Australia's dry climate. Drought is a perennial problem in many parts of the continent, so access to the rivers (when they are not dry) is vital to viticulture here. There is a strong correlation between Riverina's name, its dependence on the region's rivers and the volume-focused nature of its viticulture.