Sainsbury's (also Sainsbury and JS)-(Public, LON:SBRY), Sainsbury's is the second largest chain of supermarkets in the United Kingdom, with a 15.3% share of the supermarket sector. Founded in 1869, by John James Sainsbury with a shop in Drury Lane, London, the company became the largest retailer of groceries in 1922, was an early adopter of self-service retailing in the United Kingdom and had its heyday during the 1980s. In 1995, Tesco overtook Sainsbury's to become the market leader, and Asda became the second largest in 2003, demoting Sainsbury's to third place for most of the subsequent period until January 2014, when Sainsbury's regained second place. In April 2019, whilst awaiting to merge with rival Asda, Sainsbury's was again demoted into third place as their rival placed second.

The holding company, J Sainsbury plc, is split into three divisions: Sainsbury's Supermarkets Ltd (including convenience shops), Sainsbury's Bank and Sainsbury's Argos. The group's head office is in Sainsbury's Support Centre in Holborn Circus, City of London.

As of February 2018, the largest overall shareholder is the sovereign wealth fund of Qatar, the Qatar Investment Authority, which holds 21.99% of the company. It is listed on the London Stock Exchange and is a constituent of the FTSE 100 Index.

In April 2018, Sainsbury's and Asda were in talks of merging. Such a merger would have given the combined supermarkets an estimated 30% share of the UK grocery market. Any merger proposal resulting from these talks would be subject to investigation by the UK regulator, the Competition and Markets Authority, before taking place. On 25 April 2019, the CMA announced it would not allow the merger due to an increase in price for consumers