歐盟法之一般法律原則之中，比例原則之適用範圍廣泛，也時常被歐洲法院適用來解釋歐洲共同體（以下簡稱為歐體）內措施及行為之合法性。比例原則強調的是手段與欲達成目標之間的合適性、必要性及比例性，而達成目標之手段也必須是限制最少或最不造成損害的方式。於馬斯垂克條約生效後，比例原則與輔助原則同時被正式納入條約條文之中，成為了歐盟法之基本法律原則並具有如同憲法性的規範，可審查歐體及會員國措施之合法性。 比例原則為歐盟法重要基本原則，其法源可分為來自會員國共同一般法律原則之不成文法源及歐盟條約之成文法源，比例原則本為大陸法系之一般法律原則，於德國及法國已行之有年來保障個人之權利，之後歐洲法院於陸續案例中引用比例原則做為判決之依歸，漸漸地比例原則因其重要性而明文規定於歐體條約第5條，也因條約之明文規定被賦予了與歐洲共同體條約相同的位階，任何歐盟內的措施及立法皆不可違反比例原則。 與輔助原則之功能相同，比例原則也可限制歐體的權限以避免歐體之權限擴張而過度干涉會員國。歐體條約對於輔助原則及比例原則之設計即是作為共同體專屬權限以外領域執行權的判定依據，使歐體之資源可達到最適當的資源配置。另外，歐盟法比例原則之概念源自德國法，與德國法之比例原則相同可用來審查過度干涉私人權益及私人自由的歐體或會員國國內法規以保障私人權益，此點也是適用比例原則最終也是最重要的目的。 The main objective of this thesis is to present a legal analysis of proportionality in EU law. The principle of proportionality has been recognized as the general principle of EU law. This principle derives from the fundamental values underlying the national legal systems and it also illustrates the character of Community law as well developed by the European Court of Justice. This principle has been applied widely by the European Court of Justice to review the legality of EC acts and national measures. The principle of proportionality is laid down in the Article 5 of EC treaty by the treaty of Maastricht: “Any action by the community shall not go beyond what is necessary to achieve the objectives of this Treaty.” The principle of proportionality requires that measures adopted by Community institutions and member states do not exceed the limits of what is appropriate and necessary in order to attain the objectives legitimately pursued by the legislation. The main purpose of this principle is to protect the fundamental rights and individual freedom from being infringed by inappropriate EC and national measure. The European Court of Justice has profoundly influenced the development of the legal order of the European Community through the elaboration of unwritten general principles of law. As many important general principles of law applied by the European Court of Justice have been borrowed from German and French law, a comparative study of the various forms which this principle has assumed in German, British and French public law is presented. This thesis will introduce the development and application of this principle by the European Court of Justice and in national legal systems. In addition, the study focuses on the judicial control of subsidiarity and proportionality in expecting to explain the reasonable division of EC and national competence as subsidiarity and proportionality can be applied as legal basis to justify the competence of European Union. In the final chapter, this thesis introduces the practical application of proportional in the filed of free movement of goods and common agricultural policy in the European Union.