This document summarizes interest groups, which are organizations that try to shape public policy by influencing political decision-makers. It describes the different types of interest groups, including public interest groups focused on general welfare, and private interest groups representing specific economic interests. It also outlines the strategies interest groups use, including direct lobbying ("inside game") and mobilizing public opinion ("outside game"). Finally, it discusses concerns about unequal representation and resources among interest groups and the potential for regulatory capture.