近年來，在英語非母語的國家開設全英語課程已成為一種趨勢。為了要吸引外國學生及推動校園國際化，臺灣大專院校也開設了許多全英語課程。本研究訪談了22位公私立大專院校開設全英語課程的教師，要探討以下三個議題：開設全英語課程的動機、對學生學習狀況的認知和相應的教學策略、對台灣全英語授課政策的看法。研究發現，教師開設全英語課程動機多樣，但這些動機都與英語在學術及實業界的全球地位相關。在教學策略方面，教師常使用語碼轉換來幫助學生學習與建立良好的師生關係。本研究還發現，部分受訪教師認為全英語授課能改善學生英語程度，但也有一些教師認為全英語授課會對學科知識的學習有不利影響，尤其是對英語程度及學習動機較低的學生，影響可能更大。本研究因此建議，未來在推動全英語課程時，應仔細考量學生的一般英語能力及學門相關英語學習技巧，以做為規劃全英語課程的依據。

Using English as medium of instruction (EMI) in countries where English is not the first language has been a growing trend in the recent decades. In an effort to draw international students and promote campus internationalization, Taiwanese universities have started to offer English-medium courses; yet, little systematic research has examined their implementation and even less is known about the views and experiences of instructors teaching such courses. This interview study of 22 national and private university instructors focuses on three aspects of EMI teaching: instructors' motivations for offering English-medium courses, perceptions of student learning and teaching strategies adopted in EMI teaching, and views of the current EMI policy in Taiwan. Findings suggest that teachers offered English-medium courses for a variety of reasons, yet all the motivations seem to point to the global status of English in today's academic and professional world. The interview data also show that code switching was used as a pedagogical strategy to facilitate student learning and manage student-teacher relationship. As to the impact of English-medium teaching, although some participants were optimistic about students' English improvement, others raised concern about its detrimental effect on subject knowledge learning, particularly in students of lower English proficiency and learning motivation. An implication of this result is that students' preparedness for classes in English, including their general English proficiency and skills in English for discipline specific academic purposes, has to be carefully considered when any EMI policy is formulated at either national or institutional levels.