The National Capital Region (NCR) (French: Région de la capitale nationale, pronounced [ʁeʒjɔ̃ d(ə) la kapital nɑsjɔnal]), also known as Canada's Capital Region and Ottawa–Gatineau, is an official federal designation encompassing the Canadian capital of Ottawa, Ontario, the adjacent city of Gatineau, Quebec, and surrounding suburban and exurban areas. Despite its designation, the NCR is not a separate political or administrative entity and falls within the provinces of Ontario and Quebec.

Defined by the National Capital Act (1985), the NCR covers an area of 4,715 km² (1,820 sq mi), straddling the Ottawa River, which serves as the boundary between Ontario and Quebec. This area is smaller than the Ottawa–Gatineau census metropolitan area (CMA), which spans 8,046.99 km² (3,106.96 sq mi). Ottawa–Gatineau is the only CMA in Canada that crosses provincial boundaries.

The area that would become the National Capital Region was first settled 6 500 years ago by Algonquins, who hunted, foraged, and traded in the area through the European exploration and colonization period. The area remained relatively untouched until 1800, when Wright's Town was established as the first permanent colonial settlement in the Ottawa Valley on what is now the Quebec side of the Ottawa River. At this time and for nearly a century, the principal economic engine of Wright's Town was the Ottawa River timber trade, which saw trees felled in northern Ontario and western Quebec pushed down the Ottawa River and on towards Quebec City for shipment to the United Kingdom and United States.

After the War of 1812, amid U.S. threats to the St. Lawrence River, the British military undertook the Rideau Canal as an alternative, more defensible shipping route, which led to significant growth and land speculation in the area surrounding Wright's Town. In 1827, the settlement on the south side of the river was named Bytown in honour of British military engineer Colonel John By, who was responsible for the entire Rideau Waterway construction project. After the Canal's completion in 1832, Bytown reached a population of 1 000 and was incorporated as a city. Across the river, Wright's Town was incorporated as Hull in 1875 and the historic 1800 settlement was destroyed by fire in 1900.

The selection of Ottawa as the national capital of Canada predates Confederation and was highly contested, requiring more than 200 votes in the parliament of the United Province of Canada and provoking the Stony Monday Riot over local objections to the selection. Tensions between Anglophone Upper Canada and Francophone Lower Canada, difficulties in finding a logistically affordable and feasible capital location, and legislative stalemates all contributed to significant delays in choosing a permanent capital for the United Province of Canada. Although Bytown had been considered as early as 1849, nearly 10 years after the formation of the United Province of Canada, the final decision to establish the city as Canada's capital did not occur until 1857 (by which point it had been renamed to Ottawa). This selection was made by Queen Victoria on the advice of the Governor General of United Canada, Edmund Walker Head, and the choice was ratified by Parliament in 1859.

Construction on the parliament buildings began that December and represented the largest construction project undertaken in North America at the time. The precinct was still incomplete when the United Province of Canada, Nova Scotia, and New Brunswick united to form Canada in 1867. Parliament Hill, as the site is now known, was not completed in full until 1876.

Following the introduction of prohibition laws in Ontario in 1916, Hull became a popular spot for politicians and Ottawa residents to access alcohol legally. Although prohibition in Ontario ended in 1927, Hull's downtown continued to serve as the main entertainment district for the capital region. Hull's night life scene peaked in the mid-20th century, when upscale nightclubs landed performers such as Louis Armstrong and Tony Bennett and the Viva Disco club was named one of Playboy magazine's top ten disco clubs in North America. Wrote Brian Mulroney, "[Ottawa] visibly sagged by ten at night, just in time for residents seeking relief from the stifling boredom to cross the bridge to Hull, Quebec, where nightclubs, dancehalls, bars, and a few great restaurants provided sanctuary and stimulation." By the 1980s, however, Hull topped the list of Quebec municipalities for its high crime rate, and increased concern about the crime issue on the north side of the river led to a significant transformation of the city's downtown. The completion of Place du Portage, a federal office complex, displaced 4 000 residents and much of Hull's bar district, and the development of the Canadian Museum of History in the late 1980s spurred an aggressive zero tolerance policing campaign of what nightlife remained. By 2000, crime had dropped in downtown Hull by 75%, although the physical displacement of much of downtown Hull for federal office buildings had also led to a significant reduction in the downtown population.

In 2022, truckers protesting COVID-19 vaccination requirements for cross-border truckers began a convoy protest that ultimately converged in downtown Ottawa on January 29, 2022. Although not the first attempt to organize a protest to the national capital, the 2022 convoy was successful both in arriving in Ottawa and in staying in the downtown core, blocking major streets with trucks and heavy machinery for nearly a month. The protests also underscored challenges with the National Capital Region's complicated governance structure, as the federal government was forced to rely on the municipal Ottawa Police Service and support from the provincial government to clear the blockade.