The study of border guarding in post-war Germany has highlighted especially acts of violence by East German border guards during the Cold War. This article argues that border guarding in East and West developed in tandem, as both sides always reacted to each other and depended on each other. It shows that border guarding on both sides of the East-West divide played vital roles in state building. The article examines border guards’ complicated, often contradictory, assignments, analyzes their multi-faceted relations with and involvement in frontier society and discusses different strategies used in East and West Germany to disentangle these ties. It emphasizes the practice rather than the title of border guarding and in this way provides new variables for following state-building on ground level. The article emphasizes the crucial role of local knowledge for border guarding and discusses the relations of guards and frontier residents to this knowledge and their implications for guarding. It then analyzes different strategies employed by East and West German border guards to incorporate and/or overcome local knowledge. The article shows that ambiguous border policies employed by West German governments undermined border guarding.