Interest groups are an integral part of democratic systems: They allow individuals to become involved in the political process by advocating a cause or interest that is important to them. They are outlets for the people's expression of concern over certain issues. Interest groups in the United States have undergone many changes since the 1960s, but they still remain a strong and significant part the political process. Much can also be learned from studying interest groups through a comparative perspective.

An influential comparative analysis distinguishes two significant types of organized interest groups: institutional and associational groups. Institutional groups include large-scale organizations such as churches, militaries, and bureaucracies that serve important social or governmental functions that are not directly related to the interests of their members. Because of their size and importance, institutional interest groups are important participants in the political and policy making process in most...