Ancaster is a picturesque and historic community located on the Niagara Escarpment, within the greater area of the city of Hamilton, Ontario, Canada. This former town was founded officially in 1793 and was one of the oldest European communities established in present day Ontario along with Windsor (1749), Kingston (1780), St. Catharines (1787-89), Grimsby (1790), Niagara-on-the-Lake (1792) and Toronto (1793).

By 1823, due in large part to its easily accessible water power located at the juncture of already existing historical trading routes, Ancaster had become Upper Canada's largest industrial and commercial center. Additionally, Ancaster had at that time attracted the 2nd largest populace (1,681) in Upper Canada trailing only Kingston (population 2,500), but surpassing the populations of nearby Toronto (1,376) and Hamilton (1,000). After this initial period of prosperity beginning in the late 18th century, sudden significant water and rail transportation advancements of the early 19th century would soon better benefit Ancaster's neighbouring towns situated closer to the Lake Ontario waterfront. Stationary steam engines for industries were also being rapidly developed in the 19th century that would eventually make Ancaster's water powered industries less vital. As a result, after the 1820s, Ancaster's influence during the remainder of the 19th century would begin to wane.

From the late 19th century Ancaster's population would remain static until 1946 when new subdivisions around the village were established. The population expanded further with the completion of the Hamilton-Ancaster section of Highway 403 in 1968 and the introduction of sewer systems in 1974. After 1970, its population essentially doubled from 15,000 residents to its present-day 33,000.

Today, Ancaster's primary points of interest are its historical village core, its abundant recreational walking trails and its unique variety of restaurants, pubs and shops.

Ancaster's geography has had a very significant affect on human settlement patterns throughout its prehistory and in the present day. A highly influential geographical formation has been the Niagara Escarpment consisting primarily of limestone formed from ancient fossilized sea organisms that spans from present day New York State through Ontario to Illinois. The escarpment itself created the water power that encouraged early European settlers to gravitate to the area in the late 1700s. However, this energy source would not have been accessible if the escarpment were not navigable. This long-meandering landform generally proved to be an inhospitable transportation barrier for thousands of years for past indigenous cultures. However, a natural break in this escarpment in the precise area that would become Ancaster village had for millennia created an opportunity for people to traverse up and down the escarpment providing a relatively easy navigable land transportation gateway from the head of the lake to the surrounding land on the escarpment and vice versa.

Ancaster is the most westerly portion of the Golden Horseshoe conurbation of southern Ontario. It is generally considered to be an affluent bedroom community whose residents are typically professionals who work in downtown Hamilton, Brantford, Burlington, Oakville, Mississauga or Toronto.

The former municipality had a population of 33,232 in the 2006 census, a considerable increase from the 2001 census figure of 27,485. Development in Olde Ancaster, the historic village core, has been tightly controlled. Its current population growth and building boom occurs mainly on the east side of Highway 403 in such typically suburban commercial developments as the Power Centre and residential developments such as the Meadowlands. It has resided in the 905 area code since the latter's creation, and its telephone exchange prefixes are 648 and 304, majority being 648.