Heresy in the Heartland is a narrative case study of the 'Heresy' Affair at the University of Dayton, a series of events predominantly in the philosophy department that occurred when tensions between the Thomists and proponents of new philosophies reached crisis stage in fall 1966. The controversy culminated in a letter written by a lay assistant professor to the Cincinnati archbishop, Karl J. Alter. In the letter, the professor cited a number of instances where “erroneous teachings” were “endorsed” or “openly advocated” by four lay faculty members. Concerned about the pastoral impact on the University of Dayton community, the professor asked the archbishop to conduct an investigation. How the University weathered this controversy, the second of three major controversies to hit Catholic higher education within three years (St. John’s University, University of Dayton and the Curran affair at Catholic University of America), is of interest to faculty and administrators in Catholic higher education who continue to struggle with defining what it means to be a “Catholic” university, with the relationship of Catholic universities to the Church at large and the hierarchy in particular, and with Church teachings that conflict with the culture we live in such as immigration, the environment and sexual ethics. The story is told in chronological order by the participants in the controversy - faculty, administrators, students and clergy - using the words of those involved. Heresy in the Heartland concludes with a synopsis of what happened at the University of Dayton and draws some lessons for the future of Catholic higher education.