For decades, people living in adjacent communities along the Canada–US border enjoyed close social and economic relationships with their neighbours across the line. The introduction of new security measures during the First World War threatened this way of life by restricting the movement of people and goods across the border. Many Canadians resented the new regulations introduced by their provincial and federal governments, deriding them as “outside influences” that created friction where none had existed before. Engaging the Line examines responses to wartime regulations in several border communities, including Windsor, Ontario; Detroit, Michigan; and White Rock, British Columbia. This book brings to life the repercussions for these communities and offers readers a glimpse at the origins of our modern, highly secured border by tracing the shifting relationship between citizens and the state during wartime.