Joining NATO takes seven stages, and every one of them needs the agreement of all 32 member governments. A country asks to join, works through a reform programme, gets invited by consensus, signs an accession protocol, and then has that protocol ratified at home by each member. When the last instrument of ratification reaches the United States, which serves as depositary, the applicant becomes a full member. As of 2026 the alliance has 32 members, the most recent being Sweden in March 2024.
That is the short version. The rest of this guide explains where the rules come from, what an applicant actually has to do, and why the interesting part is not the paperwork.
Table of Contents
- How NATO Membership Works Step by Step
- What Requirements Must an Applicant Country Meet?
- What Does the Membership Application Involve?
- How NATO Membership Works During the Accession Process
- Review, reports and the reform dialogue
- Recommendation, then a unanimous decision
- Accession talks, protocol, ratification, deposit
- Why Does Every NATO Member Have to Approve a New Member?
- How Long Does Joining NATO Usually Take?
- What Happens When a Country Becomes a NATO Member?
- Can a Country Leave NATO or Be Expelled?
- Frequently Asked Questions
- Can a country join NATO without unanimous approval?
- Does the North Atlantic Treaty automatically make a new member an ally?
- What happens after a country formally applies for NATO membership?
- Does NATO membership have a standard processing time?
- Can an applicant become a NATO member before all promised reforms are complete?
- Is a NATO member automatically required to go to war?
- Conclusion
How NATO Membership Works Step by Step
Article 10 of the 1949 North Atlantic Treaty is the legal starting point. It says any European state in a position to take on the treaty’s responsibilities may become a member, and that its adherence takes effect once it deposits an instrument of ratification. Everything after that sentence is procedure.
The seven stages, in order:
- The request. A government sends a letter to the NATO Secretary General saying it wants to join.
- Intensified Dialogue. NATO assesses the country against its political and economic expectations and reports on progress.
- Membership Action Plan. The applicant adopts a structured reform programme and submits annual progress reports, a defence plan and a security sector policy.
- Invitation. The North Atlantic Council decides by consensus whether to invite the country. An invitation needs all 32 governments to say yes.
- Accession talks. The invited country negotiates its membership in Brussels, working through the same report, reform and dialogue process.
- Accession protocol. A protocol amending the North Atlantic Treaty is signed on behalf of all members by the United States.
- Ratification. Each member ratifies the protocol through its own constitutional procedures, and the new country deposits its instrument of ratification with the US State Department. That deposit is the moment membership begins.
Three aspirant countries are working through earlier versions of this route right now: Ukraine, Georgia and Bosnia and Herzegovina. An aspirant is not a member, and holds no rights or obligations under the treaty until stage seven is finished.
| Round | Year | Countries |
|---|---|---|
| Founding members | 1949 | Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, Netherlands, Norway, Portugal, United Kingdom, United States |
| Second | 1952 | Greece, Türkiye |
| Third | 1955 | Germany |
| Fourth | 1982 | Spain |
| Fifth | 1999 | Czech Republic, Hungary, Poland |
| Sixth | 2004 | Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, Slovenia |
| Seventh | 2009 | Albania, Croatia |
| Eighth | 2017 | Montenegro |
| Ninth | 2020 | North Macedonia |
| Tenth | 2023 | Finland |
| Eleventh | 2024 | Sweden |
| Stage | Main actor | Output |
|---|---|---|
| Request | The applicant government | Letter to the Secretary General |
| Intensified Dialogue | NATO | Assessment and recommendations |
| Membership Action Plan | Applicant, reviewed by NATO | Reform programme and annual reports |
| Invitation | North Atlantic Council | Unanimous invitation decision |
| Accession talks | Invitee and NATO | Reform progress and outstanding issues |
| Protocol signature | United States for all members | Signed accession protocol |
| Ratification and deposit | Each member’s parliament plus the new member | Instrument of accession deposited in Washington |
What Requirements Must an Applicant Country Meet?
The headline test is willingness and ability to uphold the treaty’s principles and contribute to Euro-Atlantic security. Behind that sit five areas of judgment drawn from NATO’s 1995 enlargement study, which still shapes how candidates are assessed.
- Democratic values. Institutions must be genuinely democratic and subject to the rule of law, with room for opposition, free media and protection of minority rights.
- Civilian control of the armed forces. The military answers to elected leaders, and no parallel armed or security structure sits outside civilian authority.
- A peaceful foreign policy. Disputes are settled through negotiation rather than force, and neighbouring countries’ borders and communities are not threatened.
- A market economy. A legal and economic framework that can support sustained defence spending, procurement and interoperability with allied forces.
- Capacity and willingness to contribute. Forces, money, secure communications and a real commitment to shared defence planning rather than a free ride.
It is worth being blunt about how this works in practice: these are shared values, not a test an applicant simply passes. A state can tick every box on paper and still not be invited, because the assessment runs on judgement as much as evidence. Two neighbouring countries may treat identical-looking facts differently because of what is happening around them.
What Does the Membership Application Involve?
Applying is a public, documented commitment. The applicant’s government says plainly that it wants membership, and NATO then puts the applicant through a demanding sequence of plans and reports before any decision is even possible.
The centrepiece is the Membership Action Plan, a reform programme the applicant designs and NATO reviews. It is a serious instrument rather than a formality: NATO publishes progress reports, and in its 2010 and 2022 updates added review measures on democratic institutions, defence and security sector governance, resilience, and partnerships. Allies can attach conditions or political declarations to an invitation, and those conditions tend to be detailed and long-lived.
NATO also gives help rather than only judgement. Members and partner countries offer mentoring on defence ministry reform, personnel policy, procurement and anti-corruption controls, often under programmes designed for exactly this purpose.
What a request does not do is create a path. There is no queue, no scoring system and no entitlement. An application can sit for a long time without any decision, which is precisely the situation aspirants describe when they talk about the process feeling opaque.
How NATO Membership Works During the Accession Process
Once an invitation is on the table, the process narrows to a fixed legal sequence. The stages below are not stages a country can compress by moving faster.
Review, reports and the reform dialogue
The North Atlantic Council reviews the applicant’s progress against the Membership Action Plan, and officials discuss what is missing and by when. This is where defence spending, command structures and civilian oversight get examined in detail, and it is usually where the most uncomfortable conversations happen.
Recommendation, then a unanimous decision
The applicant government makes its recommendation to the Secretary General. The Secretary General assesses whether the country should be invited, and the North Atlantic Council then takes the decision by consensus. Every member has a voice, and every member has to agree.
Accession talks, protocol, ratification, deposit
Accession talks run in Brussels on the same report-and-dialogue model as the Membership Action Plan. Once satisfied, the United States signs a protocol on behalf of all members, and each member ratifies it domestically: the US Senate by a two-thirds majority, and other members under whatever procedures their own constitutions require, ranging from a formal parliamentary vote to government approval alone.
One thing that trips people up: an invited country cannot negotiate bilateral deals that carve it out of the consensus process. Terms cannot be privately arranged with one member to make the other 31 objections disappear. The invitation is a decision of the alliance, and the accession protocol binds all of them equally.
The practical lesson is that ratifications are counted like votes. A protocol that has collected 31 ratifications has achieved nothing for the applicant, because the deposit requirement waits for the last instrument.
Why Does Every NATO Member Have to Approve a New Member?
NATO runs on consensus. The North Atlantic Council, which comprises one representative from each member, makes alliance decisions only when no member objects, and any single government can withhold consent.
The reason is that enlargement reshapes the alliance itself. Every new member gets a seat, a share of command structure responsibilities, access to classified information and a vote on future decisions. Members accept that risk only if they agree on the specific country. That is a political judgment about a particular state at a particular time, not an abstract assessment of eligibility.
One distinction is often lost. There is no formal veto with published criteria that a member can invoke to block a named applicant. Instead, members raise specific security concerns, and accession stalls until those concerns are resolved. The practical effect resembles a veto. The mechanism is an open political disagreement about concrete issues.
What may not be available is a way around the requirement for everyone’s agreement. A country cannot be admitted by a majority vote, and no bilateral deal with one member creates a shortcut.
How Long Does Joining NATO Usually Take?
There is no standard processing time, and NATO does not publish a target. Anyone quoting one is describing a case rather than the rules.
The pace is set by five things: how quickly the applicant completes its reforms, whether it can build defence institutions that actually function, the security situation around it, how long accession talks take to close, and whether every member is willing to say yes now. None of these is on a schedule.
Look at the phases instead of the calendar. Preparation through Membership Action Plan runs until NATO judges the country’s progress sufficient. The invitation and protocol can follow within months. Ratification is the slow, unpredictable tail, because it depends on parliamentary calendars and political weather in 32 separate countries. Recent experience has been slow: Finland and Sweden both applied in May 2022, and Sweden’s accession was completed only in March 2024.
An applicant in the middle of a war faces a different problem entirely, since members must decide what membership would actually mean before they can agree.
What Happens When a Country Becomes a NATO Member?
On the day its instrument of accession is deposited, the new member becomes a party to the North Atlantic Treaty in full. That brings collective defence obligations, planning obligations, and a permanent share of alliance decision-making.
Article 5 is the part most often misunderstood. It treats an armed attack against one member as an attack against all, and each member then takes such action as it deems necessary, including the use of armed force. That wording matters: the treaty obliges members to respond, but it leaves each government to decide what response is necessary. It is a commitment to consider collective action as an obligation, not an automatic trigger for war.
New members also join the integrated command structure, host and contribute to NATO’s forces, take part in joint exercises and planning, contribute to common NATO budgets set by consensus, and meet the alliance’s defence-spending guideline of 2% of GDP, with 1.5% as an interim floor for core defence spending and the balance on infrastructure and resilience. Most states also sign a bilateral declaration of commitment, which sets out what they will do.
On the other side of the ledger, a member gains Article 5 cover, integrated air and missile defence, intelligence sharing, joint command and communications interoperability, and a seat in the North Atlantic Council where it can block or shape consensus just like every other member.
Nothing about membership makes every disagreement military. A neighbour’s border dispute with a non-member, or a conflict where an attack is judged not to have come from a state, are exactly the grey areas allies argue about under Article 5.
Can a Country Leave NATO or Be Expelled?
Leaving is possible under the treaty itself. Article 11 allows a member to withdraw by giving written notice to the United States, with the withdrawal taking effect three months after that notice is deposited. It is the same mechanism used in the mid-1950s for countries that did not want to be tied into the alliance’s military structure.
There is no clear, established automatic process for expelling a member. The treaty contains no expulsion clause, and the nearest thing to a mechanism is that remaining members can act on the basis of the non-performance of treaty obligations. Nothing in practice sets out a fixed procedure with a fixed outcome.
Politically, withdrawal would be a much larger event than the legal step suggests. It would require coordinated decisions among the remaining members on defence plans, command structure, basing arrangements and shared projects, while the withdrawing state would lose the collective-defence relationship it joined for. Few governments have wanted to pay that cost.
Frequently Asked Questions
Can a country join NATO without unanimous approval?
No. NATO operates by consensus, and the North Atlantic Council’s invitation decision requires every member to agree. Ratification of the accession protocol is also needed from all members. There is no majority-vote route and no way to admit a country over one government’s objection, although there is also no formal veto with published criteria a member can invoke on the spot.
Does the North Atlantic Treaty automatically make a new member an ally?
Not automatically in practice. Article 5 obliges each member to take such action as it deems necessary if an armed attack occurs, which is a commitment to assist rather than a requirement to declare war. A new member also gains an integrated command structure, mutual defence planning and collective defence cover only once its instrument of accession has been deposited.
What happens after a country formally applies for NATO membership?
The request goes to the Secretary General, who adds the country to a political dialogue that becomes Intensified Dialogue and then a Membership Action Plan. The applicant adopts a reform programme, submits annual reports and a defence plan, and receives feedback. No decision to invite follows automatically. An application can run for years without a vote.
Does NATO membership have a standard processing time?
There is no published timetable, because the pace depends on reform progress, defence institution building, the security environment, the length of accession talks and political decisions in 32 capitals. Preparation and the invitation can move in a couple of years. Ratification is the unpredictable part, since one government can hold up deposit of the final instrument of accession.
Can an applicant become a NATO member before all promised reforms are complete?
Formally, membership follows the ratification and deposit sequence regardless of how much reform remains. In practice, an invitation is normally conditional, and the conditions attached to it tend to be detailed and long-lived. Reform rarely stops at membership: allies keep reviewing progress and expect continued delivery on the commitments made during the accession process.
Is a NATO member automatically required to go to war?
No. Article 5 calls on members to assist the victim of an armed attack by taking such action as each deems necessary, including armed force. Each government keeps the decision, and the treaty also leaves room for members to judge whether an attack occurred and whether it was deliberate. Membership creates an obligation to respond, not an automatic trigger for war.
Conclusion
A country joins NATO by asking, reforming, being invited unanimously, signing an accession protocol that all 32 members ratify, and depositing its instrument of accession in Washington.
The part worth remembering is why those steps are hard. NATO membership is a political and institutional transformation of a state, not an application to process, and every stage depends on reform that works in practice plus the agreement of every existing member. That is the whole answer to how NATO membership works, and it is why the countries currently waiting have no published date to plan around.
