在國際關係中領土取得方式開始於無主地的發現，時至今日，無主地幾乎已不存在，取而代 之的是島嶼糾紛的問題。然而，在聯合國憲章的架構下，對於領土糾紛並須以和平及正義的方式 解決國際爭端。因此在眾多國際法院的判例中，雖然在國際法上領土取得的方式計有：割讓、兼 併、添附、時效及先佔等方式，但可以發現有效控制原則是判決時的重要依據。因為在爭議島嶼 的各方，通常都可以提出發現與先佔的證據，但在有效統治的主權行為方面，須是在和平及持續 地行使主權中的立法及行政行為，才是符合先佔及時效等兩項中的有效控制原則。因此本文置重 點於國際法院在判決時所依的有效控制原則之客觀實踐方式，從立法與行政等二方面作一析述。

This paper argues that principle of effectiveness has been applied in judgement, and it is the basis while the court decides on a case. Territory has been taken by occupation for countries since the 15th Century. During that time, it was developed in sailing methods to cause most of the terra nullius to be found and obtained. There is no terra nullius longer to exist and island disputes are being continuous until now. In order to solve the problems peacefully, followed by UN Charter, every disputed case ought to be settled in International Court, and all cases regarding island dispute apply the principle of effectiveness when the verdict was made. That is because the parties involved in the disput can present the evidence of when they occupied the island to the court. But final verdict was made by how disputed sides show their regulation and governance on those islands. Thus, this thesis focuses on how the practices of principle of effectiveness have been practiced through legislation and administration.