The ecology of Sydney, located in the state of New South Wales, Australia, is diverse for its size, where it would mainly feature biomes such as grassy woodlands or savannas and some sclerophyll forests, with some pockets of mallee shrublands, riparian forests, heathlands, and wetlands, in addition to small temperate rainforest fragments.

Sydney is the capital city of the state of New South Wales and the most populous city in Australia. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about 80 km from the Pacific Ocean in the east to the Blue Mountains in the west, and about 80 km from the Ku-ring-gai Chase National Park and the Hawkesbury River in the north and north-west, to the Royal National Park and Macarthur in the south and south-west. Greater Sydney consists of 658 suburbs, spread across 33 local government areas. Residents of the city are colloquially known as "Sydneysiders". The estimated population in June 2023 was 5,450,496, which is about 66% of the state's population. The city's nicknames include the "Emerald City" and the "Harbour City".