We examined the role of interest groups in influencing public policy. I addressed how interest groups use lobbyist and PACs to influence legislative agendas and distinguished a PAC from an interest group. Further, we examined the types of interest groups, examples of interest groups, why people join interest groups, and how public interest groups face the "free rider" problem of those who benefit from the group's activity but do not contribute to its maintenance. We then began a study of the presidential election process. I explained the terms "invisible primary" and "closed primary" .