皈依（conversion）是宗教心理學的熱門主題，但它在不同的領域有不同定義。本文主要討論西方（主要是美國）皈依研究的歷史、發展的理論與研究方法，以及未來研究趨勢，期做為國內相關研究的基礎。本文發現皈依研究在美國有從心理學，轉往社會學，以致多元學科參與研究的發展趨勢，研究典範由「保祿經驗」的舊典範，到重視主體性與過程的新典範，並往科際整合典範轉移。百年來所發展的理論很多，大致可區分為個人、社會與文化、宗教與神學以及融合等四種取向。主要採用的研究方法為量化、質性、敘事與多層次科際整合的方法。論文最後提供研究趨勢概況，供有興趣學者參考。

Conversion is a popular topic in psychology of religion. But in different disciplines, it has different definitions. The paper aims to explore the history of conversion study, the theories and methods developed in the west (especially in the US) as the reference for further researches in Taiwan. It’s found that the history of conversion study in the US progresses from psychological, sociological to interdisciplinary approaches. The paradigm shift comes from the old paradigm, affected by Pauline experience, to the new one, focusing on subjectivity and process, and recently the paradigm of interdisciplinarity. Over one century, so many conversion theories developed have been divided into four approaches: personal, social & cultural, religious & theological, and convergent. Scholars use the methods of quantitative, qualitative, narrative and multi-level interdisciplinary paradigm to investigate conversion. For further researches, recent trends in religious conversion research are mentioned for reference.