| Term | Definition |
| interest group | an organization of people sharing a common interest or goal that seeks to influence the making of public policy |
| incentive | something of value one cannot get without joining an organization |
| solidary incentives | the social rewards (sense of pleasure, status, or companionship) that lead people to join political organizations |
| material incentives | money or things valued in monetary terms |
| purposive incentive | a benefit that comes from serving a cause or principle |
| ideological interest groups | political organizations that attract members by appealing to their political convictions or principles |
| public-interest lobby | a political organization whose goals will principally benefit nonmembers |
| social movement | a widely shared demand for change in some aspect of the social or political order |
| political cue | a signal telling a legislator what values are at stake in a vote, and how that issue fits into his or her own political views on party agenda |
| ratings | assessments of a representative's voting record on issues important to an interest group |