I investigate the multiple reasons why Islam, beginning with the character of the Prophet Muhammad, became a source of controversy in the nineteenth century, especially at a time when America was experiencing religious revivalism. In particular, I address American views of Muhammad’s prophet-hood and Islam’s position toward women and slavery. I argue that two dominant discourses on Islam informed public opinion about these subjects: an academic track that evolved from diplomatic exchanges and a popular track rooted in missionary experiences. These encounters and explanations not only shaped American attitudes about Islam, but they also exposed the historical roots of the contemporary anxieties that many Americans harbor about Islam today.