This meta-analysis reviewed research between 2012 and 2018 focused on technology-assisted second language (L2) vocabulary learning for English as a foreign language (EFL) learner. A total of 45 studies of 2,374 preschool-to-college EFL students contributed effect sizes to this meta-analysis. Compared with traditional instructional methods, the overall effect of technology-assisted L2 vocabulary learning was large (g = 0.845), suggesting that technology-assisted L2 vocabulary learning was more beneficial than non-technology-assisted instruction. Importantly, within-study comparison results indicated that technology could enhance learners' long-term vocabulary retention. Moderator analysis results highlight several variables--namely, device type, game condition, setting, test format, and reported reliability--affecting the effectiveness of vocabulary learning. Specifically, advantages were found for mobile devices and on-the-move learning, suggesting that L2 vocabulary learning may be most efficient when students use mobile phones and are not restricted by classroom settings. These variables should be considered when planning instruction in technology-assisted L2 vocabulary learning.