William Low & Co plc, popularly referred to as Willie Low's and latterly marketed as Wm Low, was a chain of supermarkets headquartered in Dundee, Scotland. Initially founded in 1868, Low's had branches throughout Scotland, North East England, Cumbria and Yorkshire. As a group, it was smaller than most of its competitors and often served small towns, although it still had several large hypermarkets. The company used to trade on its Scottishness as a unique selling point in Scotland. At one stage, the company also ran a chain of frozen food stores known as Lowfreeze. Lowfreeze was sold in 1987 to Bejam.

The remaining business was purchased by Tesco for £257M in 1994. Tesco had to compete with rival competitor Sainsbury's for the chain, with both companies looking to expand their foothold in Scotland. Following on from the takeover, the 57 William Low stores were converted to Tesco. Prior to this, there were only around 17 Tesco branches in Scotland. The purchase of Wm Low by Tesco moved them to the largest supermarket chain in the United Kingdom, beating Sainsbury's for the first time.

James Low, who was born near Kirriemuir in 1849, completed a grocery apprenticeship in Kirriemuir before moving to Dundee in 1866. Two years later, with a £300 loan from Clydesdale Bank, he opened his own grocery store at 19 Hunter Street. By 1870, he was listed in the Dundee Directory as a grocery, tea and wine merchant at 11–13 Hunter Street. At this point, James's younger brother, William, joined the business at the age of 12. A year later, James Low and William Lindsay, a local preserve, confectionery and bakery manufacturing business owner, formed a partnership, Low & Lindsay, and by 1874 they had a further branch at 304 Perth Road and had moved into wholesaling. In 1879, William Low bought the business and it was renamed William Low & Co. By 1881, the Dundee Directory listed the business as wholesale grocers and wine merchants, and the business had seven branches across Dundee. In 1884, the company opened a warehouse and headquarters at Blackness Road.

In 1885, William Rettie joined Low in partnership. Rettie was described in the 1877 Dundee Directory as a grocery and tea dealer, with stores in Rosebank Street and Dudhope Street. Rettie had married Low's sister, Annie, in 1884. The Dundee Directory of 1885 had listed that the company had eight stores. In 1888, the company opened a wholesale department in Glasgow which facilitated the opening of six stores in the city by 1895, and the expansion of the business to 46 stores across different towns, including Crieff, Inverness and Stirling. The company further expanded two years later when they purchased Farrquar and Farrell, an Edinburgh-based tea and provision merchant, for £5,000. The company continued to expand, and by the turn of the century, the business had 64 stores spread between Hawick in the south to Dingwall in the Highlands. In 1917, the company became a private limited company, with William Low as chairman. The business not only had grocery stores, but their own bakery, bottling factory and butchery departments producing goods. William Rettie died in 1922, and was replaced as managing director by his son, Archibald, while William Low died in 1936, a year after his only son. At the start of World War II, Low's had 84 branches. It was one of the larger grocery multiples, but still far smaller than the giant of Home and Colonial Stores.

By 1951, the company had recorded pre-tax profits of £57,013. In the same year, Archibald died and would be replaced by his nephew Philip Rettie, joined by William Low's grandson Ian Stewart, as joint managing directors in 1953. During the 1950s, the company started a modernisation programme with the business closing smaller non-profitable stores, replacing them with larger stores, and in 1958 opened its first self-service store, in Bellshill, as an experiment. A year later, James Millar joined as the company's financial controller. By 1960, the self-service experiment had grown to nine stores, and by a year later reported that they accounted for 34% of the company's sales. The company, however, did not follow other multiples, keeping a similar line as Sainsbury's by not adopting the issuing of trading stamps.

The company quickly expanded its self-service stores, and by 1962 the business operated 26 of them out of its portfolio of 75, with some branches having off-licences, and larger stores getting in-store butcher counters. With the increase in turnover seen at self-service stores, the company opened their first supermarkets in Aberdeen and Broughty Ferry in 1963, following these up with further supermarkets opening in Lochee, Wishaw, Arbroath, Corstorphine, Fort William, Helensburgh and Kirkcaldy. At the same time, older stores were being closed. Sandy Leslie, who became the company's retail director, stated that it was square-footage of stores, not the number of branches, by which the new criteria was measured; however, as the boss of fellow grocery chain Moores Stores also stated, the cost of developing supermarkets was expensive; there were too many supermarkets to be successful. By the end of 1969, the company had modernised the store portfolio and had nineteen supermarkets, eighteen self-service stores and five counter-service shops, a reduction of 33 stores from the total in 1962. Supermarkets in 1969 accounted for 78% of the company's profits, with the business making a pre-tax profit of £260,180, but the profit margin was being squeezed by the growth of supermarket rivals.

The company continued to grow its supermarket portfolio, and by 1972 it had grown to 31, with ten self-service stores, an increase of floorspace of 25%. James Millar stated that none of their stores were older than fifteen years. This was further accentuated with the opening of a new head office and distribution centre, at Dryburgh Industrial Estate in Dundee in October 1972, which incorporated modern data processing and warehousing methods. The company became a public limited company in 1973, launching on to the London Stock Exchange. In 1975, the company launched the first Scottish freezer chain with the opening of the first Lowfreeze store in Glenrothes. The company opened its largest supermarket to date in 1976, with a brand new store in Irvine. This was followed by the 1978 opening of the company's first superstore, in Perth, at the cost of £1.5 million. The company moved into the low end of the market in 1976, when they launched their Discount Price Policy, which was a year earlier than Tesco's own Operation Checkout. By 1980, the average size of the stores had doubled since 1972, with the company having 46 supermarkets and thirteen Lowfreeze stores. Lowfreeze by this point were generating over £5 million of the company's £74 million turnover (compared to a £9 million turnover in 1970), but the company's profit margins had fallen from 4.1% in 1970 to 2.4% by 1980.

Low's continued to grow in the 1980s, included replacing stores, such as in Kirkcaldy, where a new superstore was opened in 1981. That outlet not only sold food but also sold non-grocery products, such as bedding, and had a 125-seater restaurant. Further developments included the new 10,000-square-foot (930 m²) store at the junction of Queensferry Road and Kings Road in Rosyth, a 20,000-square-foot (1,900 m²) store in Baltic Chambers, Grangemouth and further new stores in Wishaw, Oban and Linlithgow which opened in 1982. Low's moved into the fast-food business in 1981, with the opening of McTatties, with restaurants opening in Glasgow and Edinburgh; however, this was unsuccessful and closed just a year later at a write down of £775,000. During 1982, it was reported that Hintons, another supermarket chain, were planning a takeover of Low's, and the current market valuation was £12 million. Wm Low also rose to be included as number 400 in The Times 1000, a list of top UK companies, in 1984, whereas in 1976 it was not even listed.