This document is the first comprehensive study of the characteristics of nonpublic schools in New York City. The significance of the title rests on the fact that nearly three out of ten school children in New York City attend some kind of nonpublic school. The report attempts to provide the detailed information needed to decide whether government should subsidize the parochial school system or prepare to expand the public school system to accept the inevitable influx from the parochial system if no subsidy is granted. The report includes research on enrollment trends and projections and on teacher characteristics. The study also lists alternatives other than increased government support to help the nonpublic schools. The appendix comprises a description of the study methodology and the findings comparing Catholic student performance to public student performance, a summary of State laws on nonpublic school aid, and position statements by various organizations on the topic of nonpublic school aid. (Author/DN)