本文以世界銀行之環保政策變遷為主軸，從批判的立場，首先檢視傳統國際關係理論，也就是現實主義與自由主義對於代理理論如何分別自圓其說，分析其論述與現實的差距，其次以解釋世界銀行的政策與行為轉變為案例研究，說明國際組織面對外力遊說壓力而改變其環保理念。雖然美、日、歐盟掌握世界銀行的絕大多數投票權，但是世界銀行其實不全然是強權的代理人。 本文結論是代理理論最弱之處在於難以解釋國際組織的為何改變既有之行為模式。代理理論的前提是行為人，包括委託人與代理人，均是理性而且自利的經濟人。然而在現實的國際關係，國家利益不能單純以經濟因素為計算基礎，國際組織的存在與運作也不是以效率為依歸，因此無法以代理理論有效解釋大多數國際組織的政策與行為變遷。簡言之，代理理論作為研究途徑之一，可以說明國際組織存在的理由，卻無法有效解釋其行為改變的理由。

This paper aims at examining the environmental policy change of the World Bank. A systematic criticism of traditional international theories, namely realism and liberalism, is provided to illustrate mainstream theories' limitations in explaining the gap between its discourse and reality. A case study of the World Bank's change of policy and practice on environmental protection is followed to better understand how inter-governmental organizations (IGOs) reshape their belief amidst outside lobby pressure. Although the World Bank's vast majority voting rights are controlled by the US, Japan, and EU, it in practice does not equate to the agency of super powers. This paper concludes that agency theory is too weak to explain IGOs' behavior change. Agency theory has the propositions that assumes all actors, including principal and agent, are rational and self-interests driven. The reality of international relations, however, indicates that economic factors are not the sole calculation basis for national interests, neither the efficiency as the goal of IGO's existence and operation. Therefore agency theory can not effectively explain the policy and practices of many international organizations. In a nutshell, agency theory as one of the research approaches is good for explaining the reason of IGOs' existence but lack of persuasion in explaining why they change their behavior.