This Element defines implicit language aptitude and examines tasks that can be used to measure implicit language aptitude.

It is a well-known fact that some adult second language learners learn more rapidly and/or to a higher level of proficiency than others. Some of these individual differences have been linked to differences in cognitive and perceptual abilities under the umbrella term of 'language aptitude'. The notion of language aptitude has undergone recent developments, one of which is the proposal that language aptitude includes cognitive abilities that involve implicit processes and that are advantageous in learning a language without awareness. This Element defines implicit language aptitude, examines tasks that can be used to measure implicit language aptitude, and provides an overview of relevant research in this area.