The Knights of Columbus is the world's largest Roman Catholic fraternal service organization. Founded in the United States in 1882, it is named in honor of Christopher Columbus.

There are more than 1.8 million members in 15,000 councils, with nearly 200 councils on college campuses. Membership is limited to "practical Catholic" men aged 18 or older.

Councils have been chartered in the United States (including Puerto Rico and the Virgin Islands), Canada, Mexico, the Caribbean, Germany, Guatemala, Panama, Dominican Republic, the Philippines, Guam, Spain, Japan, Cuba, and most recently in Poland. The Knights' official junior organization, the Columbian Squires, has over 5,000 Circles. All the Order's ceremonials and business meetings are restricted to members, though all other events are open to the public. A promise not to reveal any details of the ceremonials except to an equally qualified Knight is required to ensure their impact and meaning for new members; an additional clause subordinates the promise to that Knight's civil and religious duties.