This paper analyzes three major sites of contestation and local resistance to the “Blue Line” in southern Lebanon, the unofficial borderline separating Lebanon and Israel. Far from an agreement between friendly neighbors, the Blue Line is currently being drawn by the United Nations Interim Force In Lebanon (UNIFIL) and roughly marks the Israeli military’s line of withdrawal from Lebanon in 2000. Its coordinates are based on slightly adapted versions of the 1920 French and English boundary descriptions of modern Lebanon that were never been fully enforced—until now. This article will explore UNIFIL’s ongoing process of the gradual normalization of the line as the de facto border between the two warring states. This presentation will problematize the instances where once productive contested areas are transformed into abandoned, highly militarized zones in the absence of a political solution to the Arab-Israeli war. At the same time my research underlines the fragility of the Blue Line, while exploring its contradictions with the actual human geography of the land. Considering land use before and after the Blue Line demarcations, it will demonstrate the implications of enforcing this often involuntary border for the populations who are directly affected by it. By looking at the different narrations and claims to power, this paper interrogates the notion of sovereignty in a region that has undergone major political change, moving from foreign occupation to liberation, while hosting a long-term UN presence. In order to grasp the politics and meaning of contested boundaries, it will illustrate the accounts of major actors involved in the demarcation process: the Lebanese state, Israel, UNIFIL and the local population. This paper is based on ethnographic research and interviews conducted over several years with southern Lebanese citizens and officials, former officials from the Lebanese Armed Forces, and UNIFIL officials, as well as historical accounts of the borderline in question.