Accumulated recent research suggests that prior knowledge of multiple languages leads to advantages in learning additional languages. In the current article, we review studies examining potential differences between monolingual and multilingual speakers in novel language learning in an effort to uncover the cognitive mechanisms that underlie such differences. We examine the multilingual advantage in children and adults, across a wide array of languages and learner populations. The majority of this literature focused on vocabulary learning, but studies that address phonology, grammar, and literacy learning are also discussed to provide a comprehensive picture of the way in which multilingualism affects novel language learning. Our synthesis indicates two avenues to the multilingual advantage including direct transfer of prior knowledge and prior skills as well as indirect influences that result from multilingual background and include more general changes to the cognitive-linguistic system. Finally, we highlight topics that are in need of future systematic research.

When learning novel vocabulary in a third language (L3) through translations in the first language (L1), bilinguals may have more available cognitive resources and more accumulated experience in language regulation compared to when learning through translations in the second language (L2). In a study designed to test language of instruction (LOI) effects, 59 Hebrew–English bilinguals auditorily learned over two sessions 55 words in German, including three word types: cognates, overlapping in form and meaning between English and German; false cognates, overlapping in form but not meaning; and controls. Critically, half of the participants learned through their (dominant) L1 Hebrew, and half through their L2 English (which is also more similar to German). Results showed a significant LOI effect, with better learning through the (less similar) L1, especially for control items. Cognates were learned better in both LOIs, but false cognates were learned better relative to controls to a greater extent when the LOI was English. Together, results highlight the importance of LOI and item‐based language similarity during multilingual novel word‐learning.