The purpose of the Public Library Effectiveness Study was to define effectiveness for the public library institution. The research was designed not to measure effectiveness or evaluate particular libraries or groups of libraries, but rather to identify the feature or features of a public library that most directly attest to its effectiveness. The major questions the study addressed were what measures have been used to define effectiveness; what are the indicators and dimensions of public library effectiveness; whether constituent groups differ in their preferences among indicators and dimensions and in their definitions of public library effectiveness; and whether differences in the individual libraries' domains affect their constituents' preferences concerning effectiveness or organizational performance on the indicators. The study focused on public libraries and is intended to serve as a prototype for a methodology for identifying effectiveness indicators and dimensions for other types of libraries. The five chapters are: (1) "The Enigma of Effectiveness"; (2) "Methodology"; (3) "Findings Regarding Indicators and Dimensions of Effectiveness"; (4) "Findings Regarding Roles"; and (5) "Conclusions." The questionnaires used in the study, as well as the statistical findings, are found in the appendices. Also included is a 38-item bibliography. (JLB)