The stratosphere and the troposphere are coupled in many ways. Because their interactions span days to weeks (or even longer), understanding these linkages and simulating them correctly in forecast models may provide a source of sub-seasonal to seasonal (S2S) prediction skill. This chapter reviews the tropical and extratropical coupling between the stratosphere and the troposphere and summarizes the most recent research showing how adequate simulation of the stratosphere may contribute to better prediction skill in the troposphere.