In the Conciliar Declaration Nostra Aetate as well as in many subsequent Church documents, Catholic as well as Protestant, Rom 11:29 is cited as a key text for understanding Jewish-Christian relations. This article looks at the history of the interpretation of this verse, giving examples from the patristic, medieval, and reformation periods as well as from more recent exegesis. A new approach began essentially with Karl Barth during the fateful years 193-3.1942 and bore fruit in Nostra Aetate and subsequent Church (...) pronouncements, especially the Pontifical Biblical Commission's 2001 document The Jewish People and Their Sacred Scriptures in the Christian Bible. The complex and delicate interplay between historical developments, theology, exegesis, and Church teachings is particularly evident in this case. Careful interpretation of our verse answers some questions, but seems to leave others wide open. (shrink)