美国有选举人登记制度，选民首先需要登记才能投票，只有美国公民才能在联邦选举中投票。如果通过邮寄登记或者以前从未投票，则必须出示ID才能登记。这个是联邦法律的规定，适用于全部50个州。
至于投票时是否需要出示ID ，这个要求是州法的范围。有14个州在投票时不需要出示ID，但需要通过其它的方法证实自己的身份。注意一下这14州中，有4个并不是所谓“民主党州”，所以楼下情绪化的声称“民主党不让用ID”是缺乏基本的常识。
In the remaining 14 states and D.C., voters can cast a ballot in person on Election Day without showing an ID document. These states have "non-documentary" ID requirements, meaning voters must verify their identity in other ways, such as by signing an affidavit or poll book, or by providing personal information. All states have procedures for challenging voter eligibility.
Below are details on the statutory requirements for voter verification in states with non-documentary ID requirements.
Voters' Responsibilities
The three main types of non-documentary ID requirements that voters may be asked to satisfy are:
Affidavit: Voters sign an affidavit asserting their eligibility to vote and/or awareness that falsely claiming eligibility is a criminal offense. Illinois includes the full text of its affidavit in statute. Other states provide partial texts or general guidelines.
Signature: Voters must provide elections officials with a signature before casting a ballot. In most cases, this involves signing a poll book or voter registration list at the polls but there are some exceptions. For example, Oregon voters must sign the return envelope included with their mail-in ballots.
Biographical information: Voters may also be asked to provide personal information, either verbally or in writing, at the polls. In most cases, voters are asked to give their names and/or addresses. Under certain circumstances, Maryland, New Mexico and Minnesota, ask voters to provide full or partial birth dates.
加州选民登记和投票时的ID要求，可以在下面这个文件里找到。即便是加州这种基本不要求VOTER ID的州，对于某些选民在投票时也是有ID要求的。
