Online charter schools--also known as virtual charters or cyber charters--are publicly funded schools of choice that eschew physical school buildings and use technology to deliver education to students in their own homes. These schools typically provide students with computers, software, and network-based resources, while also providing access to teachers via email, telephone, web, and/or teleconference. Online charter schools deliver instruction using a radically different approach than conventional public schools. Nonetheless, critics of online charter schools worry that they might not be effective in promoting student learning. This report and its companion volumes describe the findings of the most ambitious and comprehensive study of online charter schools to date, conducted jointly by Mathematica Policy Research, the Center for Research on Education Outcomes (CREDO) at Stanford University, and the Center on Reinventing Public Education (CRPE) at the University of Washington. This volume begins with a snapshot of online charter schools operating across the country, describing their numbers, the states in which they operate, and the students they serve. The report then describes the instructional programs of online charter schools; methods used to engage students and parents, along with expectations of parental involvement; the teachers and principals of online charter schools; and their management and governance. Key findings include: (1) Student-driven, independent study is the dominant mode of learning in online charter schools, with 33 percent of online charter schools offering only self-paced instruction; (2) Online charter schools typically provide students with less live teacher contact time in a week than students in conventional schools have in a day; (3) Maintaining student engagement in this environment of limited student-teacher interaction is considered the greatest challenge by far, identified by online charter school principals nearly three times as often as any other challenge; (4) Online charter schools place significant expectations on parents, perhaps to compensate for limited student-teacher interaction, with 43, 56, and 78 percent of online charters at the high school, middle, and elementary grade levels, respectively, expecting parents to actively participate in student instruction; and (5) These findings suggest reason for concern about whether the online charter school sector is likely to be effective in promoting the achievement of its students. Appended are: (1) Survey Methods; and (2) Supplemental Table.