The border, in late Chosŏn rhetoric, was an area of pernicious wickedness; living near the border made the people susceptible to corruption and violence. For Chosŏn ministers in the nineteenth century, despite two hundred years of peace, the threat remained. At the same time, the military institutions created to contain it were failing. For much of the late Chosŏn the site of greatest concern was the northern border in P’yŏngan and Hamgyŏng provinces, as this area was the site of the largest rebellion and most foreign incursions in the first half of the nineteenth century. This study takes the northern border as the most fruitful area for an inquiry into the Chosŏn dynasty’s conceptions of and efforts at border defense. Using government records, reports from local officials, literati writings, and local gazetteers, this study provides a multifaceted image of the border and Chosŏn policies to control it. This study reveals that Chosŏn Korea’s concept of border defense prioritized containment over confrontation, and that their policies were successful in managing the border until the arrival of Western imperial powers whose invasions upended Chosŏn leaders’ notions of national defense.