In cities of decline, ruins bear a fundamentally ambiguous reality, representing scourges as well as opportunities. In Detroit, a shrinking city that was once the capital of the automotive industry, the existence of tens of thousands of ruins poses critical problems while arousing aesthetic fascination, thereby provoking fierce controversy. This article assesses the issues concerning Detroit’s ruins to pave the way for a political ethic of ruins so as to better plan for and live with ruins in cities in decline. It is based on a review of the literature on ruins and urban decline, and on a field survey conducted in Detroit in 2012 and 2013.