Plaisant, CatherineRose, AnneRubloff, GarySalter, RichardShneiderman, BenReviewing past events has been useful in many domains. Videotapes and flight data recorders provide nvaluable technological help to sports coaches or aviation engineers. Similarly, providing learners with a readable recording of their actions may help them monitor their behavior, reflect on their progress, and experiment with revisions of their experiences. It may also facilitate active collaboration among dispersed learning communities. Learning histories can help students and professionals make more effective use of digital library searching, word processing tasks, computer-assisted design tools, electronic performance support systems, and web navigation. This paper describes the design space and discusses the challenges of implementing learning histories. It presents guidelines for creating effective implementations, and the design tradeoffs between sparse and dense history records. The paper also presents a first implementation of learning histories for a simulation-based engineering learning environment called SimPLE (Simulated Processes in a Learning Environment) for the case of a semiconductor fabrication module, and reports on early user evaluation of learning histories implemented within SimPLE. Also cross-referenced as UMIACS-TR-99-34en-USTechnical Report