Interest groups attempt to affect policy by organizing people with common interests and communicating views to policymakers. Policymakers listen to public and private interest groups because policymakers need:
- money for campaign contributions;
- manpower for stuffing envelopes, putting up lawn-signs, etc;
- information, such as details on parts per million of pollutants in air.
Information plays an especially important role. Interest groups tend to focus all of their energy on a single topic, and are usually very knowledgeable about a specific area of interest.