Despite the significance of interest representation to theories of law and politics, the social organization of interest representation has not received systematic empirical analysis. Based on interviews with 776 individuals engaged in the representation of private interests concerning national policies on agriculture, energy, health, and labor, this article reports some findings concerning the social and political characteristics of representatives, the nature of their work and their relationships with client organizations. Three models of the social organization of interest representation are developed and examined: a model based on substantive expertise, an institutional targets model, and a client-based model. The findings indicate that representation is predominately organized around client interests Although lawyers constitute a significant and distinctive group among representatives, they are neither as numerous nor as active in policy making as is commonly assumed. The analysis suggests that representatives are not likely to exercise influence in the policy-making process that is autonomous from client organizations.