James D. Sinegal (born January 1, 1936) is co-founder and CEO of Costco, an international low-price membership retail chain and the largest U.S. wholesale club, headquartered in Issaquah, Washington, U.S..

He was born January 1, 1936 into a Catholic working-class family in Pittsburgh, Pennsylvania. He attended Helix High School in La Mesa, California. He earned an AA at San Diego City College in 1955. Sources vary on his higher educational attainment. Some sources indicate he earned a BA from San Diego State University (1959) and others that he dropped out of college when he found his true vocation.

After he started as a bagger at FedMart in 1954 he found he loved retailing. At FedMart, he worked his way up to executive vice president in charge of merchandising and operations. He was a vice president of merchandising for Builders Emporium 1977-1978, and an executive vice president for the Price Company 1978-1979. From 1979-1983 he worked with Sinegal/Chamberlain and Associates, a company which acted as a broker and sales representative for food and non-food products. Together with Seattle retailer Jeff Brotman, he co-founded Costco and from 1983 he has been President and CEO of Costco. His innovations made Costco the first warehouse club to include fresh food, eye-care clinics, pharmacies, and gas stations.

He was a protege of Sol Price, who pioneered the concept of the warehouse store that sells high volumes of a small variety of goods to members only. Sinegal is known for a benevolent style of management that offers employees high benefits and rewards.

In an interview published in the Houston Chronicle on July 17, 2005, he told Steven Greenhouse that he was not interested in Wall Street analysts who took issue with his care for employees and customers rather than happier shareholders. Investors might want higher earnings but Sinegal stated “We want to build a company that will still be here 50 and 60 years from now." A favorite saying of his is “you have to take the shit with the sugar”. Investors who bought $10,000 of Costco stock in 1992 had $43,564 ten years later, a return of 354% (or 15.855% annually).

He married Janet L. Dwyer in San Diego on July 21, 1962 and they have three children.

In 2009, Mr. Sinegal was considered one of "The TopGun CEOs" by Brendan Wood International, an advisory agency