The Selective Service System (SSS) is an independent agency of the United States government that maintains information on those potentially subject to military conscription (i.e. the "draft") and carries out contingency planning and preparations for two types of draft: a general draft based on registration lists of men aged 18-25, and a special-skills draft based on professional licensing lists of workers in specified health care occupations. In the event of either type of draft, the Selective Service System would send out induction notices, adjudicate claims for deferments or exemptions, and assign draftees classified as conscientious objectors to alternative service work. All male U.S. citizens and immigrant non-citizens who are between the ages of 18 and 25 are required by law to have registered within 30 days of their 18th birthdays, and must notify the Selective Service within ten days of any changes to any of the information they provided on their registration cards, such as a change of address. The Selective Service System is a contingency mechanism for the possibility that conscription becomes necessary.