It is a very American theory that is popular with political scientists. It fits well with economic principles such as Adam Smith. Its advantages are that it is comparatively neutral as to values and explains process. The theory is also called pluralism because there are many groups. It differs from a political party in that it does not try to win office.
Groups form when a disturbance occurs and people come together to resist change.
The leader is a policy entrepreneur like Ralph Nader, Lois Gibbs, Clara Barton, and David Brower. Interest groups often lobby in Washington, where their techniques are direct, grass roots, information campaigns and coalition building. Groups sometimes compete with each other and sometimes cooperate. Its tenets are that the task of the political system is to manage group conflict by establishing the rules of the game, arranging compromises, enacting the deals into law, enforcing the laws and adjudicating them. Government is like a referee calling the balls and strikes.