An old boy network is an informal system in which wealthy men with similar social or educational background help each other in business or personal matters. The term originally referred to social and business connections among former pupils of male-only elite schools, though the term is now also used to refer to any closed system of relationships that restrict opportunities to within the group. The term originated from much of the British upper-class having attended certain fee-charging public schools as boys, thus former pupils are "old boys".

In England and Wales, a public school is a type of fee-charging private school originally for older boys. They are "public" in the sense of being open to pupils irrespective of locality, denomination or paternal trade or profession; nor are they run for the profit of a private owner.