Relearning is a measure of memory that assesses how much faster material is mastered when it is studied again after a period of time. The savings in time or effort indicate that some residual memory of the original learning remains.

Hermann Ebbinghaus introduced the method in his pioneering studies of nonsense syllables. He measured the number of repetitions required for initial mastery, allowed time to pass, and then counted the repetitions needed to relearn the same list to the same criterion. The difference constituted savings. Even when conscious recall had fallen to zero, substantial savings often remained, demonstrating that memory can persist below the threshold of awareness.

Relearning is a sensitive measure that can detect memory traces missed by recall and recognition tests. It is used in research on long-term retention, the effects of sleep, and the durability of educational interventions. Everyday examples include the ease with which a once-fluent language returns after years of disuse.

Material that feels completely forgotten often reveals its residual presence when it is learned the second time more quickly.