Electoral system
Electoral rules place limits on suffrage and candidacy. Most countries's electorates are characterised by universal suffrage, but there are differences on the age at which people are allowed to vote, with the youngest being 16 and the oldest 21 (although voters must be 25 to vote in Senate elections in Italy). People may be disenfranchised for a range of reasons, such as being a serving prisoner, being declared bankrupt, having committed certain crimes or being a serving member of the armed forces. Similar limits are placed on candidacy (also known as passive suffrage), and in many cases the age limit for candidates is higher than the voting age. A total of 21 countries have compulsory voting, although in some there is an upper age limit on enforcement of the law. Many countries also have the none of the above option on their ballot papers.
Voter registration
Voter registration (or enrollment) is the requirement that a person otherwise eligible to vote register (or enroll) on an electoral roll before they will be entitled or permitted to vote. Such enrollment may be automatic or may require application being made by the eligible voter. The rules governing registration vary between jurisdictions. Some jurisdictions have "election day registration" and others do not require registration, or may require production of evidence of entitlement to vote at time of voting. In some jurisdictions registration by those of voting age is compulsory, while in most it is optional. In jurisdictions where registration is voluntary, an effort may be made to encourage persons otherwise eligible to vote to register, in what is called as a voter registration drive.