This is what NATO’s handling of a possible membership for Sweden or Finland looks like:

1) The application is received, usually in the form of a letter, signed by the Minister of Foreign Affairs.

2) The letter is being considered by NATO countries, probably at an ambassadorial meeting that is convened immediately and already on the same day decides to start accession negotiations.

3) The talks are led by one of NATO’s eight Assistant Secretaries-General, German Bettina Cadenbach, and are only expected to take a single day.

4) NATO then produces a report stating whether the countries live up to the requirements set, including a new letter from the Minister of Foreign Affairs in which the country claims to have understood what applies and still wants to move forward.

5) The NATO ambassadors then decide whether it is possible to sign the accession protocol. According to NATO, these steps can be completed within two weeks.

6) When the minutes are signed, the country becomes an “invited member” with the right to participate in all NATO meetings, but without the right to vote.

7) The minutes are then sent to the 30 Member States for final approval in each country’s parliament. It normally takes at least six months, but is expected to go faster now, given the tense security situation surrounding Russia’s war in Ukraine.

8) When all countries have done their part and the applicant country has signed and all the paperwork has been filed in Washington, you become a full member.

Source: NATO