台灣文學的主體性在1990年代大致確立。二十一世紀全球化衝擊之下，避免台灣文學在國際學術場域的孤立，開發國家文學之外的跨文學理論框架，乃重要課題。在台灣文學研究場域裡，「世界華文文學」（world literature in Chinese）、「華語語系文學」（Sinophone literature）、「世界文學」（world literature）堪稱21世紀新興的三個重要的跨文學研究框架，各有關切的重點議題，也提供了研究台灣文學的新理論框架。本論文試圖梳理這幾個研究框架的興起背景、核心概念和研究方法，並透過詩人楊牧測試此三個理論的實際運用情形，以探討此三個理論的貢獻與局限之處。楊牧創作以跨文學特色聞名，被視為華文文學創作的佼佼者，同時也是台灣詩人的代表，應該最能示範這三種跨文學理論。然而，理論實際運用卻透露了理論與實踐的落差。其中隱含的理論課題值得深究。就「世界華文文學」理論而言，無論是採用中國大陸學者主張的「共同詩學」或是「華人文化詩學」，都無法妥善處理楊牧傳承西方文學和植根台灣本土的「有根的世界感」（rooted cosmopolitanism），這意味「世界華文文學」理論必須在「共同的中華性」和「離散華人」的核心概念之外，更細膩挖掘「華文」的在地實踐。就「華語語系文學」理論而言，楊牧主張以精準優美的漢字創作，調度中國文學傳統資源的台灣文學創作觀，與「華語語系」對於台灣文學與漢文、漢文化的關係的詮釋背道而馳，提示我們重新思考漢文書寫對台灣文學創作的深層意涵。就「世界文學」而言，楊牧示範了「作為世界文學的台灣文學」如何在「世界華文文學」與「華語語系文學」所關注的身分認同政治之外，開拓台灣文學的研究議題，以及與非漢文文學社群連結的空間。除了釐清三種理論的異同和核心概念之外，楊牧與理論之間的辯證所開啟的台灣文學研究課題，亦為本文的關切重點。 In the 1990s, Taiwan literature successfully defined itself as a distinct body of writing that can be differentiated from Chinese literatures produced elsewhere. The new century brings a new task: how to situate Taiwan literature within cross-cultural contexts in an increasingly globalized world? This paper investigates three new theoretical frameworks for the study of Taiwan literature in the 21^(st) century: the so-called ＂world literature in Chinese＂, Sinophone literature, and world literature. These three frameworks are cross-cultural in the sense that they provide a conceptual scheme of understanding Taiwan literature in relation to literatures in other parts of the world. We trace the emergence of these three theoretical frameworks respectively, and identify their core concepts and methodologies. We then conduct an analysis of their strength and limitations by situating the renowned Taiwanese poet Yang Mu within the theoretical frameworks. As a well-respected and highly internationally recognized Taiwan-based literary figure of Chinese literature, Yang Mu is known for his blending of Chinese and Western literary traditions. His works draw upon different cultural traditions, and they travel across countries. Yang Mu represents Taiwan's cross-cultural writing at its best. While the contributions of the three theoretical frameworks should be duly acknowledged, it is also important that we tease out the intricate meanings of their limitations. We argue that the gap between Yang's ＂rooted cosmopolitanism＂ and the so-called ＂common poetics＂ or ＂diaspora poetics＂ proposed by the proponents of world literature in Chinese urges for a more critical reflection on the complex meanings of ＂the locale＂ for Chinese literatures in different parts of the world. We also find that Yang Mu's insistence on the use of beautifully crafted Chinese language and the importance of Chinese literary resources for Taiwanese creative writing suggests a paradigm that runs against the Sinophone critique of Chinese language and literary tradition. Finally, we examine how the conceptualization of Yang Mu as a world literature writer points to a theoretical approach to Taiwan literature that is not premised on identity politics. While only a few Taiwan writers can be identified as world literature writers, ＂world literature＂ as a concept may open a new space for connecting Taiwan literature to a large body of literary works written in languages other than Chinese.