1. Bayer, O. (2009). Tillich as a systematic theologian. In R. R. Manning (Ed.), The Cambridge companion to Paul Tillich (pp. 18–36). Cambridge, UK: Cambridge University Press.
2. Cooper, T. (2006). Paul Tillich and psychology. Macon: Mercer University Press.
3. Dourley, J. (2009). Tillich in dialogue with psychology. In R. R. Manning (Ed.), The Cambridge companion to Paul Tillich (pp. 238–253). Cambridge, UK: Cambridge University Press.
4. King, M. L. (1955/2000). A comparison of the conceptions of God in the thinking of Paul Tillich and Henry Nelson Wieman. In C. Carson (Ed.), The papers of Martin Luther King, Jr (Rediscovering precious values, July 1951–November 1955, Vol. 2, pp. 339–544). Berkeley: University of California Press.
5. May, R. (1973). Paulus: Reminiscences of a friendship. New York: Harper & Row.