This study uses fiscal data reported by traditional public school districts between 2000 and 2017 to generate descriptive estimates of the relationship between the local market share of independent charter schools and the finances of host school districts in twenty-one states. The research questions for the study are as follows: (1) On average, was an increase in the percentage of students attending independent charter schools--at the geographic school district level--associated with an increase or decrease in host districts' total revenue and/or spending per pupil?; (2) On average, was an increase in the percentage of students attending independent charter schools associated with an increase or decrease in host districts' local, state, and/or federal revenue per pupil?; and (3) On average, was an increase in the percentage of students attending independent charter schools associated with an increase or decrease in instructional and/or support spending per pupil? The results are summarized in three findings: (1) In most states, an increase in the percentage of students attending independent charter schools was associated with a significant increase in host districts' total revenue and spending per pupil; (2) In most states, an increase in the percentage of students attending independent charter schools was associated with an increase in host districts' local revenue per pupil, and in some states, it was also associated with an increase in state and/or federal revenue per pupil; and (3) In most states, an increase in the percentage of students attending independent charter schools was associated with an increase in host districts' support spending per pupil, and in some states, it was also associated with an increase in instructional spending per pupil. [Foreword was written by David Griffith and Michael J. Petrilli.]