This chapter traces the arc of NATO’s evolving force posture in the Baltic states. As such, it scrutinizes the different measures allies have undertaken to signal their willingness to fulfill Article 5 obligations vis-à-vis Estonia, Latvia, and Lithuania. The material discussed here suggests that, over time, the transatlantic alliance has approached the Baltic defense question in radically different ways. Prior to 2014, NATO governments were reluctant to establish any military infrastructure or deploy armed forces in the eastern parts of the alliance. Only after the Russian forcible takeover of Crimea did NATO begin to thicken its presence by stationing multinational troops, pre-positioning military equipment, and conducting large-scale regional military exercises. The alliance instituted the so-called “tripwire”. February 24, 2022, marked another watershed moment. In light of Moscow’s full-scale war against Ukraine, allied governments vowed to redesign their force posture on NATO’s eastern flank in a manner that could repel a Russian invasion without sacrificing territory. The following sheds new light on these moments of transformation and critically examines the challenges that remain.