Researchers explored the problem of teacher retention, especially among beginning teachers, and noted a lack of consensus on why teachers leave teaching and how to retain the teachers. Private school studies include Catholic school data, but few researchers isolated the data or used data-gathering instruments to examine Catholic school issues, such as Catholic school mission or the influence of the Catholic Church. To address the gap in the literature, Catholic schoolteachers in the Diocese of St. Augustine participated in a study to identify factors that influence Catholic schoolteacher retention. A qualitative research method with a modified Delphi design was used for gathering participant measurements from 50 full-time elementary and secondary teachers. Participants expressed significant consensus between elementary and secondary teachers on five factors influencing teacher retention: (a) commitment to the mission of Catholic schools, (b) expressing one's religious beliefs, (c) satisfaction in teaching assignment, (d) collegiality and collaboration, and (e) principal leadership style. Factors identified by prior researchers as influential on teacher retention that were not identified as being significant by the current study's population included salary, workplace conditions, class size, benefits, and professional development. The three least influential factors to teacher retention were alternative opportunities in the labor market, the hiring process, and the pastor or bishop's involvement in the school. Results may be germane to principals and administrators in reducing the present attrition rate of beginning teachers, promoting retention practices, improving the quality of education, and helping to realize the mission of the Catholic schools. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]