This document discusses learner language and interlanguage. It defines interlanguage as the developing language system of second language learners. Key points made include: (1) Learner language follows systematic developmental sequences, even when learners have different first languages; (2) Errors made by learners reflect their current understanding of the target language and are part of the learning process; (3) While first language influence exists, many errors result from generalization, overgeneralization, and simplification as learners develop rules of the new language.