This meta-analysis investigated the overall effects of glossing on L2 vocabulary learning from reading and the influence of potential moderator variables: gloss format (type, language, mode) and text and learner characteristics. A total of 359 effect sizes from 42 studies (N = 3802) meeting the inclusion criteria were meta-analyzed. The results indicated that glossed reading led to significantly greater learning of words (45.3% and 33.4% on immediate and delayed posttests, respectively) than nonglossed reading (26.6% and 19.8%). Multiple-choice glosses were the most effective, and in-text glosses and glossaries were the least effective gloss types. L1 glosses yielded greater learning than L2 glosses. We found no interaction between language (L1, L2) and proficiency (beginner, intermediate, advanced), and no significant difference among modes of glossing (textual, pictorial, auditory). Learning gains were moderated by test formats (recall, recognition, other), comprehension of text, and proficiency.