In this paper, we draw upon in-depth interviews with teachers and administrators in 18 unionized charter schools around the country to investigate teachers' motivations for unionization. Our results suggest that while mismanagement and distrust are often the proximate cause of charter unionization efforts, both material and purposive goals--greater job security and pay as well as increased voice in school decision-making--power organization drives and contract negotiations. Our evidence suggests unionization and collective bargaining agreements can create more transparency around pay and development, which teachers desired. But, sometimes unionization carried unanticipated risks for administrators--salaries increased faster than revenues and teacher development became constrained by newly formed collective bargaining agreements.