Catholic men 18 years of age or older who join the Knights belong to a council, or local unit. Many 18 to 22 year olds first join the Knights of Columbus in a college council.
Membership in the Knights of Columbus is open to men 18 years of age or older who are practical (that is, practicing) Catholics in union with the Holy See. This means that an applicant or member accepts the teaching authority of the Catholic Church on matters of faith and morals, aspires to live in accord with the precepts of the Catholic Church, and is in good standing in the Catholic Church.
Members who are over 18 years of age; a citizen of the country in which he resides; a Third Degree member in good standing; and a practical Catholic in union with the Holy See are eligible to join the Fourth Degree Knights. The Knights of Columbus also sponsors the Columbian Squires, a service and leadership training organization for Catholic young men ages 10 to 18 years old.