The Global Polio Eradication Initiative (GPEI) is “the longest, largest, most expensive global health program ever”. This chapter focuses on how the organizational dynamics among GPEI's five core partners impact the organization's problem solving and sustainability. It gives an overview of how GPEI is structured and operates and recounts the progress it has made toward polio eradication and the challenges it has encountered in finishing the job. At the global headquarters level, the core partners work together to develop GPEI's programmatic and technical strategies, establish financial resource requirements, conduct fundraising and advocacy, and coordinate and supervise GPEI's activities around the world. Overall, GPEI exhibits high levels of goal attainment, value creation for core partners, and collaboration among core partners, which they achieve through sophisticated contracting, the credible commitment of resources, and adaptability.