Impact organizations focus on changing the law rather than serving large numbers of individual clients. They do litigation, policy work, or both. Specifically, these groups adopt cases they think will have a broad impact on its area of concern.
Generally, impact organizations only hire entry-level attorneys through fellowships, either internal fellowships at the organization itself or project fellowships funded by an outside entity. Because impact organizations do complex litigation, they tend to value evidence of the ability to do research, writing, and analysis. They also look for clinical experience, internships at impact organizations, journal work, and judicial clerkships.
In some instances, an organization that is policy-oriented will take direct legal cases or selected impact litigation. In other instances, a policy-oriented organization will focus solely on research and lobbying. This is an important distinction; for example, a person who is interested in litigating a certain issue, but is interning at a policy-oriented research institution, will not receive the litigation experience desired.
Many public interest organizations are hybrids of direct service, policy and impact litigation organizations. You should research each organization thoroughly to ensure that its primary activities meet your interests.