Costco Wholesale Corporation, doing business as Costco, is an American multinational corporation which operates a chain of membership-only big-box warehouse club retail stores. As of 2021, Costco is the third-largest retailer in the world, and as of August 2024, Costco is the world's largest retailer of beef, poultry, organic produce, and wine, with just under a third of American consumers regularly shopping at Costco warehouses. As of 2025, Costco is ranked 12th on the Fortune 500 rankings of the largest United States corporations by total revenue.

Costco's worldwide headquarters are in Issaquah, Washington, an eastern suburb of Seattle, but its Kirkland Signature house label bears the name of its former location in Kirkland. The company opened its first warehouse (the chain's term for its retail outlets) in Seattle in 1983. Through mergers, however, Costco's corporate history dates back to 1976, when its former competitor Price Club was founded in San Diego, California.

Costco originally began with a wholesale business model aimed at enrolling businesses as members, then also began to enroll individual consumers and sell products intended for them, including its own private label brand. As of November 2025, Costco operates 923 warehouses worldwide, with 85% of them being in North America (United States, Canada, and Mexico).