How do unions learn to get along with each other? What factors compel them to work together and what factors tend to prevent cooperation? How do inter-union activities affect labor relations outcomes? Changed and threatening circumstances have forced those committed to the labor movement in the United States to address these questions. David Walsh sets a model for the process with his examination of unions in the airline industry, where the need for cooperation has been heightened in the era since deregulation. While the airline industry has a high rate of unionization, tradition and formal structures have hindered ties between unions. Guided by organizational theory, Walsh analyzes extensive data on pairs of unions, coalitions, and the airline union network as a whole. He finds a complex web of connections. Relations among unions in the airline industry, as elsewhere, are shaped by factors ranging from formal organizational affiliations and differences in crafts to resource inequalities and environmental threats. The ability of unions to improve the lives of workers, Walsh argues, may ultimately depend on the strength of ties across union organizational boundaries. And what is demonstrable for unions in the airline industry may prove true for the labor movement as a whole.