This article overviews research on second language vocabulary instruction with a specific focus on semantic and thematic vocabulary-clustering types. The theoretical benefits associated with both the semantic and thematic approaches, as well as the potential problems associated with them, are discussed. The conclusion drawn is that reinforcing the level of activation of target concepts during learning can lead to facilitation but only if interference from competing items is kept to a minimum. With respect to the incremental nature of vocabulary acquisition, learning programs need to boost learner engagement by embodying systematic, principled, and long-term practices.