This article examines the phenomenon of fossilization in second language (SL) learning and instruction, discussing this process as a form of simplification. Fossilization occurs when particular linguistic forms become permanently established in the interlanguage of SL learners in a form that is deviant from the target language norm and that continues to appear in performance regardless of further exposure to the target language. The article examines specific research on linguistic fossilization, looking at the nature, objects, and manner of fossilization. It also considers the point at which fossilization begins, its persistence, and the types of learners likely to be affected by the phenomenon the most. (MDM)