In 1962, Barth visited the United States and lectured at Princeton Theological Seminary, the University of Chicago, the Union Theological Seminary and the San Francisco Theological Seminary. He was invited to be a guest at the Second Vatican Council. At the time Barth's health did not permit him to attend. However, he was able to visit the Vatican and be a guest of the pope in 1967, after which he wrote the small volume Ad Limina Apostolorum [At the Threshold of the Apostles].
Princeton Theological Seminary, where Barth lectured in 1962, houses the Center for Barth Studies, which is dedicated to supporting scholarship related to the life and theology of Karl Barth. The Barth Center was established in 1997 and sponsors seminars, conferences, and other events. It also holds the Karl Barth Research Collection, the largest in the world, which contains nearly all of Barth's works in English and German, several first editions of his works, and an original handwritten manuscript by Barth.