This study examined the simultaneous effects of L2 individual difference (ID) variables (aptitude, motivation, strategy use, language processing experience, and gender) on English as a foreign language (EFL) breadth and depth of L2 vocabulary knowledge of 492 Korean university-level learners. Independent variable measures included the: (1) Korean version of the Modern Language Aptitude Test; (2) L2 Attitude/Motivation Battery; (3) L2 Vocabulary Learning Strategies Survey; and (4) L2 Language Processing Experience Survey. The dependent variables (i.e., vocabulary breadth and depth) were assessed via the Vocabulary Levels Test and Word Associates Test, respectively. Employing multigroup structural equation modeling (SEM), results revealed positive significant effects of: (1) aptitude on vocabulary breadth and depth; (2) motivation on strategy use; and (3) motivation on both dependent variables, however mediated by a significant direct effect of language processing experience on the dependent variables. There were no effects obtained for L2 strategy use nor for participant gender in the model.