The Dandenong Ranges (commonly just the Dandenongs) are a set of low mountain ranges in Victoria, Australia, approximately 35 km (22 mi) east of the state capital Melbourne. A minor branch of the Great Dividing Range, the Dandenongs consist mostly of rolling hills, rising to 633 m (2,077 ft) at Mount Dandenong, as well as steeply weathered valleys and gullies covered in thick temperate rainforest, predominantly of tall mountain ash trees and dense ferny undergrowth. The namesake Dandenong Creek and most of its left-bank tributaries (particularly the Eumemmerring Creek) originate from headwaters in these mountain ranges. Two of Melbourne's most important storage reservoirs, the Cardinia and Silvan Reservoir, are also located within the Dandenongs.

After European settlement in the Port Phillip Bay region, the range was used as a major local source of timber for Melbourne. The ranges were popular with day-trippers from the 1870s onwards. Much of the Dandenongs were protected as parklands as early as 1882, and by 1987 these parklands were amalgamated to form the Dandenong Ranges National Park, which was subsequently expanded in 1997. The range receives light to moderate snowfalls a few times in most years, frequently between late winter and late spring.

Today, the Dandenongs are home to over 100,000 residents and are popular amongst visitors, many of whom stay for the weekend at the various bed & breakfasts throughout the region. The popular Puffing Billy Railway, a heritage steam railway, runs through the hills villages of the eastern Dandenong Ranges.

The range is the remains of an extinct volcano last active 373 million years ago. It consists predominantly of Devonian dacite and rhyodacite.

The topography consists of a series of ridges dissected by deeply cut streams. Sheltered gullies in the south of the range are home to temperate rain forest, fern gullies and mountain ash forest Eucalyptus regnans, whereas the drier ridges and exposed northern slopes are covered by dry sclerophyll forest of stringybarks and box. The entire range is highly prone to bushfires, the most recent of which have been the 1983 Ash Wednesday bushfires, the 1997 Dandenong Ranges bushfires and small fires during the Black Saturday bushfires in 2009.

A number of watercourses originate in the Dandenongs, these include:

The Dandenong Ranges are home to a variety of native Australian mammal, bird, reptile and invertebrate species. Well-represented bird species include the Sulfur-crested cockatoo, Superb lyrebird, Laughing kookaburra, and Crimson Rosella. Mammals include the Short-beaked echidna, Common wombat, Sugar glider, and Swamp wallaby. Invertebrates include two species of burrowing crayfish.

The Dandenong Ranges' climate is generally cool and wet, with daily temperature variation generally low, often as low as 1 degree in the winter months. Rainfall is fairly uniform through the year, tending to peak between April and October with lower rainfall during January and February. The mean annual rainfall is between 1000 and 1500 mm, increasing with elevation and from west to east. The elevation means that daytime temperatures are typically 4 to 6 °C cooler than the lower suburbs of Melbourne to the west [1], with temperatures typically lowering by 1 °C for every 120 metres (390 ft) of elevation. Due to the elevation, upslope fog is common in the winter months. It is significantly cloudier than Melbourne, particularly in winter due to heavy orographic lifting brought about by cold fronts.