Scholars continue to study the origins of fundamentalist religion in the twentiethcentury. The importance of this study is evident to all who would seek to understand the complex political and religious currents influencing the modern world. This study focuses on the emergence of Protestant fundamentalism in Los Angeles, beginning with late nineteenthcentury trends toward religious radicalism and culminating in the splitting of radical and moderate fundamentalist groups at the Bible Institute of Los Angeles in the late 1920s. Highlighted in this study are the complex tensions between mainline Protestants and an emerging sectarian trend among those who would become militant fundamentalists, which continues to shape Protestant religion today.