後冷戰時期北大西洋公約組織所面臨的任務，從對抗以蘇聯為首的共黨集團威脅，轉化為保障中東歐區域的安定。決定北約是否能面對這一新的挑戰，甚至北約能否繼續生存，將取決於北約與中東歐國家的關係。 北約應否在令踐結束後向東擴張，長期以來一直是國際關係學者與相關決策者辯論的議題，爭辯的焦點集中在俄羅斯對北約東擴的反應，北約擴張對中東歐的利弊，擴張的成本與北約的功能及替代性各方面的爭議。綜合而言，這場幾手朝兩個完全相反方向的激辯，主要的立論基礎著重在理性主義的考量上。 一九九○年代是北約擴張的關鍵年代，從九○年代初期對東擴的模糊政策，到九○年代中期以後北約的擴張政策逐漸明朗，並逐漸加快擴張的速度。事實上北約的擴張採取的是雙軌方式，亦即循序漸進的將中東歐國家納入北約的範疇，但同時也以不排除俄羅斯參與北約的高度模糊性，來降低東擴的障礙。 以北約擴張的實際進程來檢驗學術上正反意見的辯論，可以發現前述辯論疏忽了非理性主義做為解釋北約擴張工具的可能，本文即試圖藉由對於北約擴張正反意見的整體評論來找出這個軍事聯盟在環境變遷之後仍持續擴張的適當解釋。

　　　　　In the Post-Cold War ear, the North atlantic Treaty Organisation is faced with changing missions ahead, shifting from the deterrence against the threat pose by the Soviet-led Communist bloc to the assurance of stability in Central and Eastern Europe, a region that was once antagonistic to the alliance. Whether NATO would be able to adapt to the new challenges, a question that would be closely linked with its survival, would be based upon the organisation's relationship with the CEE nations. The issue on whether NATO should extend it membership to the CEE has been a focus of scholarly debates among theorists and practitioners in international relations. The pros and cons of the enlargement of the alliance revolve around rational factors such as Russia's reaction to the enlargement, advantages and weaknesses caused by the CEE's NATO membership, transaction costs of the enlargement, and alternatives, if any, to NATO expansion. The 1990s turned out to be a critical era for the evolution of NATO enlargement. The alliance seemed undecided in its policy towards expansion in the first half of the decade, and not until the mid-1990s and NATO started to declare, unambiguously, its intention to expand the organisation. The alliance has since adopted a "two-track" policy, namely extending its membership to the CEE step-by-step, while mitigating obstacles towards the enlargement posed by Russia by creating partnership with Russia that would no rule out the prospects of future, though remotely, embership for Moscow. By verifying the literature of the debates centred on NOTO enlargement with the actual developments of the policy, this article attempts to show that the rational factors proposed by the current literature cannot offer satisfactory explanations for the organisation's extension and that irrational factor, instead, can be seen as a useful alternative for sound interpretations.