How is the national electoral register created?

Act No. 24 from 16 May 2000 Concerning Parliamentary Elections to the Althing

Article 2

Applications for the right to vote pursuant to item (b) of paragraph 2 of Article 1 should be sent to [the National Registry]1) on a proper form indicating the applicant's name, ID number, last domicile in Iceland, address abroad, and when he or she moved from Iceland. An application shall at the same time include a statement from the applicant to the effect that he or she is still an Icelandic citizen. [The National Registry] provides these application forms, which must be readily available at Icelandic Embassies and at the offices of the permanent missions of Iceland, at consular offices and at the offices of honorary consulates. Applications received by the [National Registry] more than one year before the lapse of the right under item (a) of paragraph 2 of Article 1 should not be taken into consideration. If an application is satisfactory, the [National Registry] will notify the applicant and the relevant municipal authority thereof. A decision that an individual is to be added to the electoral register is effective for a period of four years from the proximate 1 December following the submission of the application.

OSCE/ODIHR Needs Assessment Mission Report, Iceland, Presidential Elections, 25 June 2016

All citizens that are at least 18 years of age have the right to vote. Voter registration is passive and Registers Iceland maintains a central database of registered voters based on the population register. Voters residing abroad remain in the voter register for eight years following their departure, after which they must actively register for elections. After elections are called, Registers Iceland provides extracts of the voter list to the municipalities, which split them by polling ward. The lists are made available for public scrutiny ten days before election day. Corrections, except changes to location or residence, can be made up to and on election day. Voters can also check their entries via an online platform.