承認是國際法之基礎，並且屬於一項許久之前就已存在的制度。承認之最早使用係出現於中世紀時期，因當時的政治實體為了成為基督教國家家庭或族群的獨立成員，遂請求教宗的承認。雖然教宗權力在中世紀未衰退，但歐洲少數強權國家在19世紀上半葉承續此一角色。於現代的實踐中，承認之給予係完全交由現存的國家自行決定，即由國家政府的行政部門判斷，並且該判斷對司法部門具有拘束力。國家實踐的多樣化與學者論辯的分歧性皆顯示，承認的政治理論尚未發展至法律理論之階段。羅德派特（H. Lauterpacht）的承認權利與承認義務學說至今仍未被廣泛接受。在國際法文獻裡經常被廣泛討論的承認理論，包括構成說與宣示說。構成說早先在國際法實證原則的影響下獲得了一些支持。在19世紀，國際法通常被視為僅適用於歐陸文明化國家。其他國家則必須經由歐陸國家的承認才能加入。但可能出現一些窘境，因構成說主張不被承認之國家於國際法上不具有權利與義務，這是一項無法令人接受的論述。其次，一些國家承認、但其他國家不承認之國家地位也呈現一種矛盾現象。於20世紀盛行的觀點應屬宣示說。宣示說的歷史淵源可以回溯至自然法學派與自決權的概念。宣示說主張，國家在承認之前即已存在，並且承認行為只是對既存事實表達正式認知而已。易言之，承認僅宣布一項既存事實，並表達一特定實體已擁有國際法要求的必要資格。

Recognition is to be the basis of international law. It is a system that has existed for a long period. Its earliest utility appeared to be in the Middle Ages when a political entity, in order to admit an independent member of the family of Christian nations, required the Pope's formal recognition. Although the power of the Pope waned at the end of the Middle Ages, that similar role was assumed by the European Great Powers in the first half of the nineteenth century. In the contemporary state practice, the grant of recognition is exclusively left to the decisions of the executive branch of national governments and its decisions would be binding upon the judicial branch's judgments. Both the diversity of state practice and the difference of scholar's view show that the political theory of recognition has not evolved to the extent of a legal theory. The H. Lauterpacht's theory that there are a right to recognition and a duty to recognition up to now has not been broadly accepted. There are two theories that have been widely discussed in the legal literatures. The constitutive theory in history has gained some support under the impact of the positivist doctrine of international law. During the nineteenth century, international law was usually considered as just applying to the European civilized states. Otherwise, the other states were only admitted through the recognition of those states. However, the constitutive theory could show some embarrassments. For instance, it insists that an unrecognnized state has neither rights nor obligations in the international law. This is an unacceptable proposition. In addition, the status of the state recognized by some states on the one hand and not recognized by others on the other hand shows a very strange scene. The most prevalent theory in the twentieth century and nowadays is the declaratory theory. Its historical origin can be retroactively dated back to the natural law school and the concept of the right of self-determination. In accordance with this theory, a state exist before the recognition, and the act of recognition just formally acknowledges an already existing fact, that is, recognition merely declares that a particular entity has the necessary qualifications of a state as laid done in the international law.