Acting on a general perception that attempts to remove, restrict, or alter materials found in public and public school libraries have increased during the past decade, the Senate Committee on Appropriations for the Departments of Labor, Health and Human Services, and Education and related agencies directed the National Commission on Libraries and Information Science (NCLIS) to conduct a study to determine the extent of censorship in American public and school libraries over the past decade and to assess how society is responding to it. This report provides an analysis and summary of existing publicly available data; no new survey was undertaken due to time and fiscal constraints. An executive summary is followed by the full report, which is divided into three sections. Section 1, the introduction, includes the charge to NCIIS, a glossary of terms related to censorship, and the methodology used in the study. Section 2 describes censorship activities in public and school libraries from 1975 to 1985, and provides a summary and analysis of the data, as well as a summary of 11 significant court decisions involving public school library censorship cases. Section 3 presents the findings and conclusions. A list of challenged materials and an annotated selected bibliography of 96 works related to censorship in public and public school libraries conclude the study. (THC)