The American Express Company (Amex) is a card company and card issuer, an American multinational financial services company specialising in payment cards. Amex provides the back office, clearing and settlement of transactions (purchases, cash withdrawals) between the banks (POS terminals, ATMs and card issuers) connected to the Amex system, while at the same time issuing cards to its customers. Amex is one of the world's most valuable companies and one of the 30 components of the Dow Jones Industrial Average. The company's logo, adopted in 1958, features a gladiator or captain, whose image appears on the company's well-known travelers' checks, debit cards and credit cards. Its headquarters are located in the American Express Tower in New York City. Amex is the largest traveler's cheque company in the world. Founded in 1850 as an express mail dispatcher, the company introduced financial and travel services to customers in the early 1900s. American Express developed its gold card in 1958, its green card in 1966, its platinum card in 1969 and its centurion card in 1984.

Until 2020, OTP Bank issued AMEX cards in Hungary, but this has now been discontinued.

In most of Europe Amex cards are accepted, and in most countries there are banks that issue Amex cards. However, in Europe it is better to carry a Mastercard or Visa card as well, as these are more widely accepted.

American Express accounted for 22.9% of total US credit card transactions in dollars (in 2016), with 56.4 million cards in the US and 121.7 million cards in circulation worldwide in 2021. The international acceptance of American Express is much lower than that of its competitors. For example, American Express cards are accepted in more than 160 countries worldwide, lagging behind Visa and Mastercard, which are accepted in more than 200 countries.