The Dutch Roman Catholic theologian Erik Borgman (1957), who developed a cultural theology, was appointed as a visiting professor at the liberal Protestant theological Mennonite Seminary in Amsterdam. In this article, his progressive Roman Catholic theology is compared to a liberal Protestant approach. The historical backgrounds of these different types of theology are expounded, all the way back to Aquinas and Scotus, in order to clarify their specific character for the sake of a better mutual understanding. Next, the convergence of these two types of theology in the twentieth century is explained with reference to the philosophy of Heidegger. Finally, the difficulties posed by postmodern philosophies to both a progressive Roman Catholic theology and a liberal Protestant theology are shown. It is asserted that both types of theology claim that the insights of their particular tradition can be relevant beyond this tradition to modern and postmodern humans.