Grand juries consist of 16 to 23 jurors (it's up to the judge), but 12 yes votes are always required for an indictment. Grand jurors are selected from the same voter registration rolls used to pick ordinary federal jurors. Hundreds are summoned when a new jury is needed and then the judge excuses people who would find it especially burdensome to give up two or three days a week for a year and a half. As a result, grand jurors are generally retirees, the unemployed, or government employees.