If you don't mind me commenting, mofur, I'm American, and my experience is that you recieve a notice to report to jury duty. People are then randomly chosen from the jury pool to be interviewed for a particular trial. You don't know what trial until you are interviewed, or you may never be called from the pool at all.
It is possible to be excused from jury duty if you have a legitimate reason. You simply write a letter to the judge explaining your reason, and you will recieve a letter either excusing you or notifying you to report for duty.