I believe these resources are commentaries on or studies of the catechisms rather than catechisms per se.
- Ratzinger, Joseph. Gospel, Catechesis, Catechism: Sidelights on the Catechism of the Catholic Church. Translated by Adrian Walker. San Francisco: Ignatius Press, 1997.
- Nevin, J. W. History and Genius of the Heidelberg Catechism. Chambersburg: Publication Office of the German Reformed Church, 1847.
- Ratzinger, Joseph Cardinal, and Christoph Schönborn. Introduction to the Catechism of the Catholic Church. San Francisco: Ignatius Press, 1994.
- Reformed Church in the United States. Tercentenary Monument: In Commemoration of the Three Hundredth Anniversary of the Heidelberg Catechism. Chambersburg, PA.;New York: M. Kieffer & Co.; Lindsay & Blakiston; A. D. F. Randolph, 1863.