What are the formal steps and timeline for a country to join NATO?
Executive summary
NATO accession is a multi-step political and legal process that begins with a country declaring its intent and can include a Membership Action Plan (MAP), accession talks, preparation and signature of accession protocols, and ratification by all existing members — with final membership effective only after every ally deposits instruments of accession with the United States [1] [2] [3]. Timing varies widely: some applicants used MAPs and took many years (Montenegro took about seven years from MAP invitation to accession), while recent accessions (Finland, Sweden) showed the process can be faster or sidestep MAP depending on politics; ratification alone typically takes about a year but can be longer if national procedures or objections slow it [2] [3] [4].
1. What NATO says: Article 10 and the Alliance’s “open door”
NATO’s charter (Article 10) establishes an “open door” policy: the Alliance decides by consensus whether to invite a country to join and no third country has a formal role in that decision; NATO frames enlargement as strengthening Euro-Atlantic security and insists any decision requires unanimous agreement of Allies [1]. NATO lists aspirant countries publicly (for example, Bosnia and Herzegovina, Georgia, Ukraine in recent years) and documents past rounds of enlargement to show how accession has been implemented [1].
2. The usual formal steps, as described in reporting and reference guides
Reporting and institutional explainers synthesize a common sequence: [5] an aspirant notifies NATO of its desire to join and may enter preparatory relationship programmes (e.g., Partnership for Peace); [6] NATO and the aspirant hold consultations and may invite the country into a Membership Action Plan (MAP) to guide reforms; [7] when Allies agree, NATO prepares accession protocols to amend the Washington Treaty; [8] each NATO member signs and then ratifies those protocols under their national procedures; [9] membership is consummated only when every Ally deposits its instrument of accession with the US government [10] [2] [3]. Sources note some aspirants may proceed directly to accession talks without MAP if circumstances permit [3] [2].
3. What a Membership Action Plan (MAP) means in practice
MAP has traditionally been NATO’s formal programme to help candidates meet political, economic and military criteria and to manage reforms; most post‑Cold War entrants used MAPs, and Bosnia and Herzegovina was the only country in a MAP as of 2025 [11] [2]. However, MAP is not mandatory: Finland and Sweden’s recent experiences show NATO can adapt practice to political realities — Sweden’s bid was delayed politically even after an invitation, illustrating that membership is as much about Allies’ domestic ratification politics as technical reforms [2] [4].
4. Ratification: the choke point that determines timing
Once accession protocols are signed, each Ally must ratify them under its national rules — parliaments, referenda or executive actions depending on the country — and unanimity is required. The House of Commons briefing and encyclopedic overviews stress ratification is often the most protracted phase: in practice, the ratification phase “usually takes about a year” but can be longer if reforms remain outstanding or if individual Allies raise objections [2] [3]. Recent cases demonstrate this: Sweden’s membership was delayed by a small number of Allies’ objections despite broad political agreement elsewhere [4].
5. Timeline variability — examples and what determines speed
Enlargement rounds show wide variance: some countries joined within a relatively short period after invitation, while others (Montenegro, earlier MAP users) took many years to meet benchmarks and secure ratification [2] [1]. Key determinants of timing are: the aspirant’s pace of political, legal and military reforms; whether Allies view accession as strategically desirable; and domestic ratification politics within each Allied capital [12] [3].
6. Political realities, disputes and alternative views
Sources underline two competing realities. NATO presents enlargement as technical and consensus-based [1], but independent analyses emphasize that enlargement is intensely political: national parliaments, bilateral disputes (e.g., objections by a single Ally), and geopolitical tensions (noted in reporting around Sweden/Finland and Ukraine) can speed up, slow down, or block accession [4] [13]. Some commentators and allies argue membership should be conditional on resolving bilateral disputes and completing reforms; others point to fast-tracking where strategic necessity is perceived [3] [2].
7. Limitations and gaps in the available sources
The sources provided summarize procedures and cite examples through 2024–2025, but they do not offer a single, legally binding checklist with strict timeframes; nor do they specify step‑by‑step templates that apply in every case — timing remains case‑specific and driven by political consensus among Allies [2] [1]. Available sources do not mention an exhaustive timeline for every accession nor do they list every legislative step for each Ally’s ratification process (not found in current reporting).
Conclusion: Joining NATO follows a recognized sequence — declaration of intent, possible MAP, accession protocols, national ratifications and deposit of instruments — but the calendar is political as much as procedural; unanimous approval by all Allies and national ratification are the final and often decisive steps [1] [2] [3].