反托拉斯法之功能係為防止企業意圖控制價格、壟斷市場而使市場競爭秩序受到限制，以維護市場公平競爭，其效力原則上應限於各該國，但於外國所為之行為而在內國發生限制競爭之效果者，此時對於於內國發生限制競爭之效果者，內國之反托拉斯法得否適用該域外行為，即生問題。此一涉及內國反托拉斯法有否域外效力或內外國反托拉斯法立法管轄權之分配之課題，非針對單純內國案件，乃為超國界法之範疇，尤其在經貿關係全球化之今日，此一課題更顯重要。本文即就此一重要之超國界法課題，先從屬地主義與效果理論之理論層面，再從美國法與歐洲法之實務層次加以論述，之後論及我國法之現況，最後以檢討與展望加以結論。

The enforcement of antitrust law against foreign companies for conduct outside the territory, which affects internal commerce, has for many years caused considerable international tension. The jurisdiction of antitrust law extends to restraints of foreign concerns whether or not the objectionable conduct occurred in the territory, if the requisite “effect” on internal commerce is present. This article will generalize the territorial principle and the effect doctrine in the extraterritorial application of antitrust law in U.S. and EU judicial determinations and also conclude a reasonable boundary line of the extraterritorial application of antitrust law.