An interlanguage is an emerging linguistic system that has been eveloped by a learner of a second language (or L2) who has not become fully proficient yet but is only approximating the target language: preserving some features of their first language (or L1) in speaking or writing the target language and creating innovations. An interlanguage is idiosyncratically based on the learners' experiences with the L2. It can fossify in any of its developmental stages. The learner creates an interlanguage using different learning strategies such as language transfer, overgeneralisation and simplification.