Performance evaluation is a part of quality management for any organization. Specifically, a library defines her missions and goals first; draws up her resource allocation and action plans accordingly; then exploits performance evaluation to measure if the achievement of her plans meets her missions and goals. Recently, due to the change in political, economic and societal environment, general public, communities, and governments require public libraries to present their achievement; therefore, performance measurement is increasingly important. This article explicates the definition of performance measurement, introduces related projects conducted in Germany, USA, and Taiwan. Finally, it describes outcome measurement.