面對跨國企業在「數位經濟」下的各種利潤移轉行為，財政部相繼提出「跨境電子勞務交易課徵營業稅規範」及「外國營利事業跨境銷售電子勞務課徵所得稅規定」以為因應。其中，有關跨境線上交易的「所得稅」課徵議題，由於直接衝擊居住國政府及來源地國政府間的稅捐管轄權競合問題，因而各國政府在處理上顯得較為謹慎。本文以下首先介紹外國營利事業在我國境內課徵所得稅的相關規範，同時指出我國所得稅法在規範上的先天缺陷，以及傳統「常設機構標準」在「數位經濟」下可能面臨的衝擊與挑戰；其次，本文將參考德國文獻，針對線上交易的服務類型及其境內所得稅課徵進行討論，試圖以更廣泛的視野，為我國跨境線上交易的所得稅課徵，提供未來修法上的可能想像；同時針對「跨境電勞所得稅規定」，進行規範性的評析，特別是在現行所得稅法的框架下，是否還可以容許稅捐稽徵機關考量外國營利事業銷售貨物或電子勞務與我國的「經濟關聯性」或「境內利潤貢獻程度」，進而改變境外居住者在我國的應納稅額，本文也將予以釐清；最後，本文將以德國「跨境授權使用軟體規範」為例，深入檢討跨境授權使用軟體及資料庫的境內所得稅課徵議題；並以此為鑑，期許我國未來在跨境線上交易的稅捐立法上，毋忘三思而後行，謀定而後動。

Facing profit shifting behavior of multinational enterprises under the “digital economy”, the Ministry of Finance (MoF) have successively published the “Directions on the Levying of Business Tax on Cross-Border Electronic Services Transactions” and “Decree on Income Taxation of Cross-Border Electronic Services Provided by Foreign Enterprises”(the “ITCES Decree”). Among these regulation, the ITCES Decree relates to income taxation of cross-border online transactions, which usually brings disputes over tax jurisdiction between the source country and the country of residence. Therefore, governments usually deal with this issue more prudently. This essay starts with the relevant regulation of income taxation of foreign profit-seeking enterprise in Taiwan, and points out the defects of Income Tax Law, as well as the impact and challenge traditional “Permanent Establishment Standard” might face under the “Digital Economy”; then, this essay discusses the different types of online transactions and the domestic income tax levied on them, referring to German literature, and provides suggestions for law amendment in the future; besides, this essay also carries out a normative evaluation and analysis of the ITCES Decree, especially against whether the tax authority is allowed, under the current Income Tax Law, to tax foreign profit-seeking enterprise upon the “Economic Relevance” or “Onshore Profit Contribution Ratio” of their sale of goods or electronic services in Taiwan; finally, this essay takes Germany’s “Limited Tax Liability and Withholding Tax at Source on the Cross-Border Provision of Software and Databases” as an example, making an in-depth review of the issue of domestic income tax levy on cross-border licensing of software and databases; with the reflection above, this essay looks forward to a careful and deliberate law amendment for tax on cross-border online transactions.