In 1992, California became the second state in the nation to adopt a charter school law. California now leads the nation in both number of charter schools and charter school enrollment, with more than 1,200 charter schools serving 620,000 students in the 2017-18 school year. California is also home to more charter school authorizers than any other state, with 336 different entities overseeing charter schools, including 294 local school districts, 41 county offices of education, and the State Board of Education. Though relatively understudied, authorizers are a critical governance structure for charter schools that influence the growth and quality of a state's charter school sector. Charter school authorizers play three essential roles: (1) vetting applications to open new charter schools, (2) monitoring existing charter schools, and (3) deciding to renew or close charter schools (Vergari, 2001). In this report, the authors review the state of charter school authorizing and oversight in California, compare its policies and practices to those of other states, and compile the best available evidence on how effective California's approach to authorization is in each of these three areas.