This paper addresses the intersection of coalition formation, judicial strategies, and regulatory politics. Coalitions are a low-cost means for assembling minority interests into more powerful blocs. However, in most cases in regulatory politics, judicial strategies are high cost efforts. I argue that coalitions among interests form one basis for judicial participation, but that participation manifests in an array of coalition microstructures. For any one event, the microstructure of the interest group coalition varies, but across events the coalitions take on general forms. I offer evidence for a variety of coalition microstructures in interest group participation as amici curiae (friends of the court) in cases before the United States Supreme Court. The evidence is drawn from the case of the Group of Ten, a stable, long-term coalition of environmental interest groups that operated from 1981 to 1991.