This article describes how formation of the Allies Against Asthma coalitions was influenced by community context, history, leadership, membership, structure, processes, and other factors. Based on member surveys, key informant interviews, and self-assessment tools, results indicate that three coalitions developed from existing coalitions, and four formed in response to funding. The coalitions took an average of 12 months to form and completed 98% of formation tasks. Funding, technical support, and networking among grantees promoted formation. Although cultures, geographies, lead agencies, and years of experience differed, coalitions developed similar structures and processes. Two of three new coalitions took the longest to form, highlighting the need for flexibility and technical assistance when funding new coalitions.