Markham (/ˈmɑːrkəm/) is a city in the Regional Municipality of York within the Greater Toronto Area of Southern Ontario, Canada. It is approximately 30 km (19 mi) northeast of Downtown Toronto. The city is the fourth-most populous community within the Greater Toronto Area after Toronto, Mississauga, and Brampton and is

York Region's most populous municipality.

In the Canada 2016 Census, Markham held a population of 328,940. The municipality is also Canada's 16th largest city. Markham changed its status from town to city on July 1, 2012.

The city gained its name from the first Lieutenant-Governor of Upper Canada, John Graves Simcoe (in office 1791–1796), who named the area after his friend, William Markham, the Archbishop of York from 1776 to 1807. The first European settlement in Markham occurred when William Berczy, a German artist, and developer, led a group of approximately sixty-four German families to North America. While they planned to settle in New York, disputes over finances and land tenure led Berczy to negotiate with Simcoe for 64,000 acres (260 km2) in Markham Township in 1794. Through much of Markham's history, the community has been described as an agricultural community. A turn towards a more urbanized community within the township began after World War II when the township began to feel the effects of urban encroachment from Toronto. The completion of Highway 404 during the mid-1970s accelerated urban development in Markham.

As of 2013 tertiary industry mainly drives Markham. As of 2010, "business services" employed the largest proportion of workers in Markham – nearly 22% of its labor force. The city also has over 1,000 technology and life-sciences companies, with IBM as the city's largest employer. Several multinational companies also have their Canadian headquarters in Markham, including Honda Canada, Hyundai, Advanced Micro Devices, Johnson & Johnson, Avaya, IBM, Motorola, Oracle, Toshiba, Toyota Financial Services, Huawei, Honeywell, and Scholastic Canada.