Issue frames in policy discourse and news reporting regularly influence citizens' political opinions. Yet, we only have a limited understanding of how and among whom these framing effects occur. I propose a dual-process model of issue framing effects arguing that we must understand mediators of framing (the how question) in connection with individual-level moderators of framing (the whom question). Experimental results show that issue framing affects opinion through different psychological processes depending on who the receiver of the frame is. Among the moderately politically aware or those having weak political values, framing effects were mediated through processes of changing importance of considerations as well as changing content of considerations. Among the highly aware, only the importance change process mediated framing effects, while there were no framing effects among those least aware or those having strong values.