The Acadians (French: Acadiens [akadjɛ̃], [akad͡zjɛ̃]) are an ethnic group descended from the French who settled in the New France colony of Acadia during the 17th and 18th centuries. Most Acadians live in the region of Acadia, as it is the region where the descendants of a few Acadians who escaped the Expulsion of the Acadians (aka The Great Upheaval / Le Grand Dérangement) re-settled. Most Acadians in Canada continue to live in majority French-speaking communities, notably those in New Brunswick where Acadians and Francophones are granted autonomy in areas such as education and health.

Acadia was one of the 5 regions of New France. Acadia was located in what is now Eastern Canada's Maritime provinces, as well as parts of Quebec and present-day Maine to the Kennebec River. It was ethnically, geographically and administratively different from the other French colonies and the French colony of Canada. As a result, the Acadians developed a distinct history and culture. The settlers whose descendants became Acadians primarily came from the southwestern region of France, also known as Occitania, such as the rural areas of Poitou-Charentes and Aquitaine (Gascony). In some cases Acadians intermarried with Indians of the region, such as Mi'kmaq and other Wabanaki tribes, and were considered Métis people.

During the French and Indian War, (known in Canada as The Seven Years War ) British colonial officers suspected that Acadians were aligned with France, after finding some Acadians fighting alongside French troops at Fort Beauséjour. Though most Acadians remained neutral during the war, the British, together with New England legislators and militia, carried out the Great Expulsion (Le Grand Dérangement) of the Acadians between 1755 and 1764. They forcefully deported approximately 11,500 Acadians from the maritime region. Approximately one-third perished from disease and drowning. In retrospect, the result has been described as an ethnic cleansing of the Acadians from Maritime Canada.

Most Acadians were deported to various British American colonies, where many were put into forced labour or servitude. Some Acadians were deported to England, some to the Caribbean, and some to France. After being expelled to France, many Acadians were eventually recruited by the Spanish government to migrate to Luisiana (present-day Louisiana). These Acadians settled into or alongside the existing Louisiana Creole settlements, sometimes intermarrying with Creoles, and gradually developed what became known as Cajun culture.

In time, some Acadians returned to the Maritime provinces of Canada, mainly to New Brunswick. The British prohibited them from resettling their lands and villages in what became Nova Scotia. Before the American Revolutionary War, the Crown settled Protestant European immigrants and New England Planters in former Acadian communities and farmland. After the war, it made land grants in Nova Scotia to Loyalists. British policy was to establish a majority culture of Protestant religions and to assimilate Acadians with the local populations where they resettled.

Acadians speak a variety of French called Acadian French, which has a few regional accents (for example, Chiac in the southeast of New Brunswick, or Brayon in the northwest of New Brunswick). Most can also speak English. The Louisiana Cajun descendants tend to speak English, including Cajun English, and/or Louisiana French, a relative of Acadian French from Canada.

Estimates of contemporary Acadian populations vary widely. The Canadian census of 2006 reported only 96,145 Acadians in Canada, based on self-declared ethnic identity. However the Canadian Encyclopedia estimates that there are at least 500,000 of Acadian ancestry in Canada, which would include many who declared their ethnic identity for the census as French or as Canadian.