For nearly two decades teachers unions and charter schools have defined the major points of conflict over school reform, forming an "us vs. them" narrative that pits one against the other. By design, charter schools are free from many state and district regulations--including collective bargaining agreements. And when students enroll in charter schools, money from traditional public school districts follows, reducing the resources available in the bargaining process. As a result, many union leaders view rapid growth in charter schools as a threat to their very existence--depriving them of members and weakening the power of collective bargaining. Previous research was unable to inform why teachers in charter schools choose to unionize, whether and how contracts evolve over time in ways that mimic or differ from those that exist in traditional school districts, and if unionization and bargaining address teachers' stated motivations and priorities. In this report, the authors set out to understand trends in charter school unionization, document teachers' motivations for unionization, assess whether and how collective bargaining agreements in charter schools differ from those in traditional school districts, and explore variation in contracts over time. They tracked changes in the rate of unionization in charter schools across the nation, interviewed 21 teachers and administrators involved in recent negotiations across 9 cities with semi-structured interview protocols, and analyzed collective bargaining agreements in unionized charter schools. They learned: (1) Nationally, charter schools are no more likely to be unionized today than they were a decade ago, but unionization is gaining traction in some localities; (2) Breakdowns in trust between administrators and teachers, and teachers' desire for influence, spark unionization efforts, but dissatisfaction with work conditions can fuel them; (3) Collective bargaining agreements in charter schools are similar to district contracts, but they are more likely to preserve key flexibilities; (4) Unionization can enhance teachers' sense of efficacy in working with administrators, but it rarely resolves all of the issues underlying bargaining campaigns; and (5) Administrators and unions can be more effective in their work with teachers.