Giant Tiger Stores Limited is a Canadian discount store chain which operates over 260 stores across Canada. The company's stores operate under the Giant Tiger banner in Alberta, Manitoba, New Brunswick, Nova Scotia, Ontario, Prince Edward Island and Saskatchewan; under the GTExpress and Scott's Discount banners in Ontario and under the Tigre Géant banner in Quebec.

As of 2021, the chain reported annual sales of roughly $2 billion and employed about 10,000 people. Its headquarters are located on Walkley Road in Ottawa. In 2018, the company opened a 600,000-square-foot (55,742 m²) distribution centre in Johnstown, halfway between Montreal and Toronto, at the intersection of Ontario's Highway 401 and Highway 416.

It is a participant in the voluntary Scanner Price Accuracy Code managed by the Retail Council of Canada.

In the mid and late 1940s, Giant Tiger founder Gordon Reid, who was then in his early twenties, was a travelling salesman for an importer in the United States. In the American Midwest, Reid first saw discount stores. Discount stores were a new concept at the time. He was particularly impressed by Uncle Bill's, a chain headquartered in Cleveland, Ohio, which was one of his clients. The discount store concept did not yet exist in Canada, and it therefore represented a business opportunity.

Reid reports that he was also inspired by Frank Woolworth’s continent-wide success, half a century earlier, in creating hundreds of profitable Five-and-Dime stores. Reid’s own retail experience, dating back to his first job as a teenager, had been in department stores rather than in discount, but his mother had worked behind the luncheon counter at a Woolworth’s in downtown Montreal.

Reid stated, four decades later, that he had believed, even at this early stage, that it would be possible to build a Canada-wide chain based on this model. Asked by a reporter whether he had ever imagined that Giant Tiger would eventually have the success it was then enjoying, Reid stated, "Yes. That was the original intention. The idea for the business came when I was a travelling salesman. I saw the discounters growing. My original inspiration was the F. W. Woolworth Co., obviously that was a big chain. So this was always the plan."

Key head office personnel were co-owners of Giant Tiger Stores Limited. Initially, Giant Tiger’s head office was quite small; and ownership was therefore shared among a small number of people. By 1980, ownership had been shared between Reid and ten key employees. Gordon Reid has stated that Canada’s agricultural cooperative movement was his inspiration for this innovation. Making his employees into part-owners of the company ensured that, as in the co-op movement, all employees would share a common interest in maximizing profits.

Giant Tiger #1, opened in Ottawa's historic Byward Market in 1961, was company-owned. The first franchised Giant Tiger was opened by Jean-Guy Desjardins in Maniwaki in 1968. As Reid would explain it forty years later, from the moment the change was made, "the [Maniwaki] store made money and I didn't have to do anything. [Jean-Guy Desjardins] did the advertising, he found the location, he merchandised it to suit his customers, he did everything ... And, I thought, 'by golly, that's a good system.'"