A particularly controversial topic in current education policy is the expansion of the charter school sector. This paper analyzes the spillover effects of charter schools on traditional public school (TPS) students in New York City. I exploit variation in both the timing of charter school entry and distance to the nearest charter school to obtain credibly causal estimates of the impacts of charter schools on TPS student performance, and I am among the first to estimate the impacts of charter school co-location. I further add to the literature by exploring potential mechanisms for these findings with school-level data on per pupil expenditures (PPE), and parent and teacher perceptions of schools. Briefly, I find charter schools significantly increase TPS student performance in both English Language Arts and math, and decrease the probability of grade retention. Effects increase with charter school proximity and are largest in TPSs co-located with charter schools. Potential explanations for improved performance include increased PPE, academic expectations, student engagement, and a more respectful and safe school environment after charter entry. The findings suggest that more charter schools in New York City may be beneficial at the margin, and co-location may be mutually beneficial for charter and traditional public schools.