As Americans, our judicial civil duties are limited but are very important. First and foremost, all citizens can be called upon at any time to serve on a jury. Most of the time this service is required, but there are a few exceptions (personal illness, family illness, schooling out of state) that can excuse someone from fulfilling this duty. Far more rare (but also more important) is the duty to show up to court to serve as a witness. The formal notification of your service as a witness is known as a subpoena.