Public interest groups differ from other types of interest groups in that they claim to serve the common good, not just their own particular interests. they were the first political associations to use the strategy of direct mailing. they were the first group to abandon lobbying and take up only grassroots activism.

unlike other interest groups, their status is like that of a charity, not a political organization.

unlike other interest groups, they have no membership requirements and allow any member of the public to join.