Most, if not all, of the more than 250 players that NFL teams will draft later this week will have something in common: They are college students.

For draft eligibility, the NFL requires that players “have been out of high school for at least three years and must have used up their college eligibility before the start of the next college football season.” There are rare instances in which teams sign players who didn’t attend college as undrafted free agents, although those players are outliers and don’t tend to receive big contracts.