This study shows how performance measurement can be developed to take advantage of the most advanced computer software and hardware now available. The "Toolbox" study was commissioned by the European Commission (EC) and undertaken by De Montfort University in partnership with Essex County Libraries and the Library and Information Statistics Unit at Loughborough University (England). Performance measurement systems to benefit library management should include mechanisms for: monitoring performance, monitoring the results of innovation, identifying problems and opportunities, evaluating alternative options, and planning. In most advanced countries libraries have a fully computerized catalog, an integrated computer system, open access, and devolved budgets. Part 1 is an introduction. Part 2 considers shortcomings in current performance indicators and proposes a general strategy to make the best use of present computer power. Particular attention is focused on calculating cost data. Part 3 outlines proposals to initiate and improve particular performance measures. Performance measures are described for analysis of staff time, speed in acquiring items and satisfying requests, user analysis, numbers of active users, use of information or reference services, space provision, stock quality analyzed by age and title counts, interlibrary loans and acquisitions, and service points and opening hours. Part 4 considers the applicability of these techniques to libraries of different type and size, particularly academic and public libraries. Figures show cost benefit data, request statistics, and weighted average calculations for bookstock. (SWC)