In this paper we characterize the transmission mechanism in a monetary union with segmented financial markets. We conclude that the impact of a monetary policy shock on the aggregate variables of the union depends on the degree of financial market segmentation. We also find that a monetary injection yields heterogeneous allocations across countries. In particular, a temporary monetary policy shock leads to permanent trade balance and current account effects. Further, the consumption correlation between countries is smaller than the output correlation. The degree of financial market segmentation and the endogenous distribution of liquidity in the monetary union are key to understanding this equilibrium.