Australian Kriol, also known as Roper River Kriol, Fitzroy Valley Kriol, Australian Creole, Northern Australian Creole or Aboriginal English, is an English-based creole language that developed from a pidgin used initially in the region of Sydney and Newcastle in New South Wales, Australia, in the early days of European colonisation. Later, it was spoken by groups further west and north.^{[clarification needed]}

The pidgin died out in most parts of the country, except in the Northern Territory, where the contact between European settlers, Chinese people and other Asian groups, and the Aboriginal Australians in the northern regions has maintained a vibrant use of the language, which is spoken by about 30,000 people.^{[not verified in body]} Despite its similarities to English in vocabulary, it has a distinct syntactic structure and grammar. It is a language in its own right and is distinct from Torres Strait Creole.

The first records of the progenitor to Kriol, a pidgin called Port Jackson Pidgin English (PJPE), are found from the 1780s, with the pidgin being used for communication between the white settlers around Port Jackson and the local indigenous population. During that period, relations between the native Australians and Europeans were strained and often violent. Aboriginal people fiercely defended their lands. However, the control of lands was eventually seized by the settlers when a cattle company acquired much of the area. The settlers became more determined to take full control of the land from the native people and carried out a campaign to do so.

European settlement in the Northern Territory was attempted over a period of about forty years. Settlement finally succeeded in 1870 with the founding of Darwin, and an influx of English and Chinese speakers followed. To communicate between these two groups and the local Aboriginal people, many pidgins developed throughout the territory based on PJPE. By 1900, PJPE had developed into Northern Territory Pidgin English (NTPE), which was widespread and well understood.

Then, by 1908, NTPE would creolise into Australian Kriol, starting first in the Roper River Mission. One reason for this was the resettlements and land seizures that nearly annihilated the indigenous population, as they created drastic social change. Another reason was that the Anglican mission had between 70–200 people at any given times from eight different aboriginal ethnic groups who spoke different native languages. Although adult members of these groups were multilingual because of frequent meetings and ceremonies, the children communicated almost entirely in NTPE, except for close friends and family with whom they would have shared a home language. But NTPE would not have been sufficient for communication so the children naturally expanded the pidgin until it creolised into Australian Kriol. Children from these communities disseminated English features throughout their communities. Although the relations between the missionaries and Aboriginal people were friendly, the missionaries were not responsible for the development of Kriol. In fact, they tried to introduce Standard English as the official language for the mission, which the Aboriginal children used in class and with the missionaries, but Kriol still flourished.

Not all speakers of NTPE would switch over to Australian Kriol though as many after 1908 continued to speak NTPE. Kriol gradually spread and this spread was significantly sped up by policy changes made after World War 2 as well as changes caused directly by World War 2. This process of creolisation entailed a massive increase in the lexicon as well as a complexification of the grammar of the language. When NTPE speaking communities creolised not all NTPE speakers would start speaking Kriol for those in more peripheral parts of the Kriol speaking area their NTPE was heavily influenced by English so when it creolised it became a dialect of Australian Aboriginal English heavily influenced by Kriol.

Kriol was not recognised as a language until the 1970s, as it was regarded as a dialect of English.

A Kriol orthography began development in 1973, shortly after the Australian Government's announcement of an education policy using English, Kriol, and Aboriginal languages. Though a small amount of work had been done in 1967 by Mary Harris and Margaret Sharpe, their work had not been built on, and Kriol orthography has little influence from their work. From 1973 to 1975 linguists John Sandefur and Sharpe worked on the orthography with only limited involvement from native speakers of Kriol. By mid 1976 Kriol speakers from a Ngukurr school had become involved in the project, ensuring the orthography would work for both the Bamyili and Ngukurr dialects, as at the time these two dialects were the most known amongst the wider Australian establishment. By November 1976 the orthography was complete and was launched with a four-week Kriol writers' course in Bamyili and Ngukurr schools.