The generation effect refers to the finding that subjects who generate information (e.g., produce synonyms) remember the information better than they do material that they simply read. Meta-analytic techniques were used to summarize 445 effect sizes over 86 studies, thereby assessing the magnitude and 11 potential moderators of the generation effect. The size of the generation effect across the 86 studies was .40--a benefit of almost half a standard deviation of generation over reading. The variability of the effect size due to moderator type was substantial, and we attempted to use this information to clarify several theories that have been proposed to explain the generation effect.