The Black Thursday bushfires were a devastating series of fires that swept the state of Victoria, Australia, on 6 February 1851, burning up 5 million hectares (12 million acres; 50,000 square kilometres; 19,000 square miles), or about a quarter of the state's area. Twelve human lives were lost, along with one million sheep, thousands of cattle and countless native animals.

"The temperature became torrid, and on the morning of the 6th of February 1851, the air which blew down from the north resembled the breath of a furnace. A fierce wind arose, gathering strength and velocity from hour to hour, until about noon it blew with the violence of a tornado. By some inexplicable means it wrapped the whole country in a sheet of flame fierce, awful, and irresistible."

Bushfires in Australia are a widespread and regular occurrence that have contributed significantly to shaping the nature of the continent over millions of years. Eastern Australia is one of the most fire-prone regions of the world, and its predominant eucalyptus forests have evolved to thrive on the phenomenon of bushfire. However, the fires can cause significant property damage and loss of both human and animal life. Bushfires have killed approximately 800 people in Australia since 1851, and billions of animals.

The most destructive fires are usually preceded by extreme high temperatures, low relative humidity and strong winds, which combine to create ideal conditions for the rapid spread of fire. Severe fire storms are often named according to the day on which they peaked, including the five most deadly blazes: Black Saturday 2009 in Victoria (173 people killed, 2000 homes lost); Ash Wednesday 1983 in Victoria and South Australia (75 dead, nearly 1900 homes); Black Friday 1939 in Victoria (71 dead, 650 houses destroyed), Black Tuesday 1967 in Tasmania (62 people and almost 1300 homes); and the Gippsland fires and Black Sunday of 1926 in Victoria (60 people killed over a two-month period). Other major conflagrations include the 1851 Black Thursday bushfires, the 2006 December bushfires, the 1974–75 fires that burnt 15% of Australia, and the 2019–20 bushfires. It is estimated that the 2019–2020 bushfires led to the deaths of at least 33 people and over 3 billion animals.The gradual drying of the Australian continent over the last 15 million years has produced an ecology and environment prone to fire, which has resulted in many specialised adaptations amongst flora and fauna. Some of the country's flora has evolved to rely on bushfires for reproduction. Aboriginal Australians used to use fire to clear grasslands for hunting and to clear tracks through dense vegetation, and European settlers have also had to adapt to using fire to enhance agriculture and forest management since the 19th century. Fire and forest management has evolved again through the 20th and 21st centuries with the spread of national parks and nature reserves, while human-caused global warming is predicted to continue increasing the frequency of blazes.