Electronic performance support system (EPSS) technology provides a powerful mechanism for helping end-users operate complex systems. This article describes and discusses some research we have undertaken to explore their potential within academic library systems. Based on a needs analysis, an EPSS for supporting library users was designed and implemented. An evaluation of the system showed that an experimental group of EPSS users was more successful than a control group in performing library tasks, showing that aided task performance was better than unaided. Implications of the results and future work are discussed. (Contains 9 figures.)