Captions provide a useful aid to language learners for comprehending videos and learning new vocabulary, aligning with theories of multimedia learning. Multimedia learning predicts that a learner's working memory (WM) influences the usefulness of captions. In this study, we present two eye-tracking experiments investigating the role of WM in captioned video viewing behavior and comprehension. In Experiment 1, Spanish-as-a-foreign-language learners differed in caption use according to their level of comprehension and to a lesser extent, their WM capacities. WM did not impact comprehension. In Experiment 2, English-as-a-second-language learners differed in comprehension according to their WM capacities. Those with high comprehension and high WM used captions less on a second viewing. These findings highlight the effects of potential individual differences and have implications for the integration of multimedia with captions in instructed language learning. We discuss how captions may help neutralize some of working memory's limiting effects on learning.