The Mallee is a sub-region of Loddon Mallee covering the most north-westerly part of Victoria, Australia and is bounded by the South Australian and New South Wales borders. Definitions of the south-eastern boundary vary, however, all are based on the historic Victorian distribution of mallee eucalypts. These trees dominate the surviving native vegetation through most of Mallee, (except for swamps and areas along waterways). Its biggest settlements are Mildura and Swan Hill.

At the 2011 census, the four local government areas (LGAs) that are usually thought to define the district had a combined population of 88,178. The area of these same four LGAs is 40,183 square kilometres (15,515 sq mi).

An area of South Australia immediately to the west of the Victorian Mallee region, also once covered with mallee scrub, is commonly referred to as the "Murray Mallee" or "the Mallee".

The Mallee is, for all practical purposes, completely flat and very low-lying: in fact, for long geological periods the whole region was inundated by the ocean. Most of the Mallee consists of sand dunes that have been deposited as a result of movement of sand from the interior of Australia during arid glacial periods of the Quaternary. The soils are generally very infertile and sandy: the better ones on more stabilised sand dunes in the east are slightly loamy and pink to light brown and have been able to support wheat and barley growing as a result of the development of superphosphate and other fertilisers. In the west, the soils are unconsolidated sands, much less alkaline than in the east, and not generally able to support any grain cropping.

The Mallee has no surface drainage: the native vegetation has so high a rooting density that the rainfall of most years is easily absorbed and the porous sandy soils mean that any excess in an exceptionally wet year will recharge groundwater supplies which tend to be highly saline. Flow from the Wimmera River to the south supplies Lake Hindmarsh and, very occasionally (in 1918, 1956 and 1975), overflows to the north. The Murray River is, thus, the only source of fresh water for the region and is consequently overburdened by intensive irrigation. As of 2019, 61% of the area utilizes drip irrigation.

The climate of the Mallee is the hottest and driest in Victoria owing to its inland location. Rainfall is usually only produced by the most vigorous frontal systems or by occasional penetration of tropical air in the summer. Average annual rainfall shows a well-defined north–south gradient: Mildura averages only 267.9 millimetres (10.55 in) per year but Hopetoun in the south receives around 370 mm (15 in). Variability, however, is quite high : in 1973 the Mallee averaged as much as 650 mm (26 in) but in 1982 only 115 mm (4.5 in). Temperatures in summer are generally very hot: during the Early 2009 southeastern Australia heat wave, Hopetoun reached 48.8 °C (119.8 °F) and the average maxima in January and February are 32.7 °C (90.9 °F). In July, maximum temperatures average 15.4 °C (59.7 °F), but minima average 4.4 °C (39.9 °F) and frosts are very common.

In his 1939 paper on the physiography of North-Western Victoria, E.S. Hills stated that: "the chief factors involved in the distinction between the Mallee and the country south and east of it are precipitation, evaporation, rock type, porosity of the superficial deposits, drainage away from high areas and supply of water from streams that rise in regions of higher rainfall."

At the 2011 census, the Mallee had a population of 81,544, most of which live close to the Murray River in the district's two cities, Mildura and Swan Hill. These and other settlements within the municipalities based on these centres contain over two-thirds of the region's population. Ouyen and Murrayville are the main settlements of the central Mallee, while Kerang, Cohuna, Hopetoun and Birchip are the major towns in the south.