Cover Illustration: U.S. border fence separating San Diego, California, from Tijuana, Mexico, looking south from the San Diego side, 2012. Today we hear a lot of talk about walls and the need to reinforce national boundaries. In this year’s AHR Conversation, six scholars from a wide range of fields and periods take up the subject of “Walls, Borders, and Boundaries in World History.” While attentive to contemporary issues, the discussants offer both a historical and a global perspective on this set of concerns. The fence shown in the cover illustration divides the beach at Friendship Park, part of California’s Border Field State Park on the U.S.-Mexico border. Border crossings going in both directions between the cities of San Diego and Tijuana number 300,000 a day. Photograph © Andrew Lichtenstein. Courtesy of the photographer.