Which? is a United Kingdom brand name that promotes informed consumer choice in the purchase of goods and services by testing products, highlighting inferior products or services, raising awareness of consumer rights, and offering independent advice. The brand name is used by the Consumers' Association, a registered charity and company limited by guarantee that owns several businesses, including Which? Financial Services Limited (Which? Mortgage Advisers), Which? Legal Limited and Which? Limited, which publishes the Which? Papers.

The vast majority of the association's income comes from the profit it makes on its trading businesses, for instance subscriptions to Which? magazine, which are donated to the campaigning part of the organisation to fund advocacy activity and inform the public about consumer issues. Which? magazine maintains its independence by not accepting advertising, and the organisation receives no government funding. The Consumers' Association is the largest consumer organisation in the UK, with over 573,000 subscribers to its magazine.

Until 2006, the association used prize draws similar to those of Reader's Digest to attract subscribers, but following criticism they were discontinued. The Association attracts subscribers to its publications with free mini-guides and trial offers.