This chapter studies optimal monetary stabilization policy in interdependent open economies, by proposing a unified analytical framework systematizing the existing literature. In the model, the combination of complete exchange-rate pass-through ('producer currency pricing') and frictionless asset markets ensuring efficient risk sharing, results in a form of open-economy 'divine coincidence': in line with the prescriptions in the baseline New-Keynesian setting, the optimal monetary policy under cooperation is characterized by exclusively inward-looking targeting rules in domestic output gaps and GDP-deflator inflation. The chapter then examines deviations from this benchmark, when cross-country strategic policy interactions, incomplete exchange-rate pass-through ('local currency pricing') and asset market imperfections are accounted for. Namely, failure to internalize international monetary spillovers results in attempts to manipulate international relative prices to raise national welfare, causing inefficient real exchange rate fluctuations. Local currency pricing and incomplete asset markets (preventing efficient risk sharing) shift the focus of monetary stabilization to redressing domestic as well as external distortions: the targeting rules characterizing the optimal policy are not only in domestic output gaps and inflation, but also in misalignments in the terms of trade and real exchange rates, and cross-country demand imbalances.