The chapter argues that since the mid-1960s, Austria and Hungary managed to create a "masterpiece of European detente". It first focuses on how this evolving example of European detente reshaped the common border from the mid-1960s to the beginning of the 1970s. Next, the chapter places the history of the opening of the "Iron Curtain" at the Austrian-Hungarian border in 1989 in a long-term perspective and assesses its consequences for the fall of communism in East-Central Europe. Then, it explains why and how the "Iron Curtain" became more permeable in the 1970s and 1980s. Following this, it assesses the origins of the so-called "world-passport" that in 1988 provided all Hungarians with the right to travel and shows its enormous effects. Finally, the chapter argues how European detente in the Austrian–German–Hungarian scenario managed to overcome the "Iron Curtain" and thereby contributed to ending the Cold War.