Which? is a product-testing and campaigning charity with a magazine and website run by Which? Ltd (formerly known as the Consumers' Association, which is still the official name of the charity). Based in the United Kingdom, it engages in advocacy campaigns on various consumer protection issues and aims to promote informed consumer choice in the purchase of goods and services, by testing products, highlighting inferior products or services, and raising awareness of consumer rights. It maintains its independence by not accepting advertising or freebies; everything bought for testing is paid for at full price. Which? is funded entirely by its subscribers and has no shareholders. This justifies its tagline of "Independent expert advice you can trust".

Which? carries out systematic testing of consumer products and financial services, the results of which are published in reports in the magazine and on the website. The Which? 'Best Buy' label is well-known and respected by industry and consumers. Tests are carried out on consumer items like electrical goods, cars, and computers, as well as health and financial services, and supermarkets. Testing highlights issues such as reliability and value-for-money.

The Which? website features a Reviews section (review site) for products and services, and also has a free Advice section with "over 450 comprehensive guides giving straightforward, expert advice you can trust".

The magazine also raises awareness of trading it believes goes against the interests of consumers. It offers advice on consumers' legal rights and reports on legal cases where it has fought for members' rights. In the May, 2003 issue, for example, the back page featured a couple who won compensation from their credit card firm after purchasing a poor holiday. Another case featured was a life assurance company which had not maintained customer records properly and was forced to pay compensation. Which? also communicates regularly with the OFT and recently brought a "supercomplaint" against private dentists in the UK. In the past, Which? has been criticised for its use of junk mail prize draws, similar to Reader's Digest, to gain additional subscribers and since mid-2006 prize draws have been discontinued [1]. New subscribers are now attracted via free mini-guides and trial offers.

Which? Ltd produces several other specialist magazines apart from the main Which? magazine. These include Which?Holiday, "Which?Money", Which?Computing , Which?Car, and Which?Gardening .

Which?Books also publishes the annual Good Food Guide, and several Essential Guides including Giving and Inheriting, Divorce and Splitting Up, Be your own Financial Advisor, The Pension Handbook, Working for yourself and an annual Tax Handbook.

Which? also provides a telephone legal advice service (Which?Legal) and recently launched the Which?Local site for recommending local trades and services, and an energy switch service named "Switch with Which?".

Another new initiative in 2008 was to make Which? 'Essential Reports' available online at the Which? Digital Store. Each standalone Adobe Acrobat (pdf) guide is available to download for a one-off payment of between £1 and £8, offering an alternative opportunity for consumers to benefit from Which?'s product testing without a monthly subscription. Titles include "Choosing a digital camera", "Using your PC" and the Good Food Guide.

Today, Which? is the largest consumer organisation in the UK, with over 1 million subscribers