Interest groups, sometimes called pressure groups or special interest groups, exist for the purpose of lobbying and generally exerting pressure to influence public policy in the direction of the group's chosen interest or interests. There are various ways to classify interest groups. Some, for instance, are groups of individuals, while others are groups of groups, such as businesses, corporations, state entities, charities or churches.
Probably the most common way of classifying groups is by the policy areas they seek to influence. Some of the largest and most powerful are economic interest groups such as the National Association of Manufacturers or the U.S, Chamber of Commerce. There are also interest groups which themselves represent parts of government, often seeking to bring local issues to the fore at a federal level. These include the National Conference of Mayors and the National League of Cities.
One of the most common types of interest group is the single-issue group. In the case of hotly-debated public issues, such as abortion or gun-control, there will generally be interest groups on both sides of the issue, working directly against each other. For instance, the National Rifle Association lobbies against gun control, while the National Coalition to Ban Handguns advocates for it. Similarly, there are many religiously-based interest groups, but also those which campaign for secularism, and the separation of Church and State.