"The customer is always right" is a motto or slogan which exhorts service staff to give a high priority to customer satisfaction. It was popularised by pioneering and successful retailers such as Harry Gordon Selfridge, John Wanamaker and Marshall Field. They advocated that customer complaints should be treated seriously so that customers do not feel cheated or deceived. This attitude was novel and influential when misrepresentation was rife and caveat emptor ('let the buyer beware') was a common legal maxim.

Variations of the phrase include le client n'a jamais tort ('the customer is never wrong'), which was the slogan of hotelier César Ritz, first recorded in 1908. A variation frequently used in Germany is der Kunde ist König ('the customer is king'), while in Japan the motto okyakusama wa kamisama desu (お客様は神様です), meaning 'the customer is a god', is common.

American department store entrepreneur Marshall Field is sometimes credited with coining the phrase, as is his one-time employee Harry Gordon Selfridge, and the marketing pioneer John Wanamaker. The earliest known printed mention of the phrase is a September 1905 article in the Boston Globe about Field, which describes him as "broadly speaking" adhering to the theory that "the customer is always right". A November 1905 edition of Corbett's Herald describes one of the country's "most successful merchants", an unnamed multimillionaire who may have been Field, as summing up his business policy with the phrase. During the construction of Harry Selfridge's London store in 1909, the British press ridiculed the project and its policy, unheard of in London, that the customer would be "always right".

However, John William Tebbel was of the opinion that Field never himself actually said such a thing, because he was "no master of idiom". Tebbel rather believed it probable that what Field would have actually said was "Assume the customer is right until it is plain beyond all question that he is not.". Field's "Rules of Business", reported in his obituary in the Chicago Daily Tribune, contain no such rule; the Tribune describing Field's business methods, inherited from Potter Palmer, as being those of the customer having a right, to take goods on approval, and to return them for a refund without quibbling.

Alfred Pittman had observed before Tebbel, in 1919, that this was in fact the correct form of the Field quote. Pittman wrote in an article on Field's business policies that "the exact version of the saying" was "Assume that the customer is right until it is plain beyond all question that he is not.", going on to explain that when customers are treated this way they usually do the right thing, and in practical terms it thus becomes a policy of the customers always being right.

César Ritz's le client n'a jamais tort ("the customer is never wrong") was first recorded in 1908, and is sometimes cited as the origin of the term.

In the 21st century, social media users and TikTok videos began claiming that the phrase had been abbreviated from "The customer is always right, in matters of taste", with some directly attributing this longer quotation specifically to Selfridge. Fact-checking website Snopes found no evidence for this.

The phrase was coined at a time when most stores operated on the principle of caveat emptor, and could not always be trusted by customers. Writer Howard Vincent O'Brien described the more customer-friendly policy as "breaking down the barriers of mistrust which from time immemorial have existed between men in the exchange of goods".