Stephen Krashen

Stephen Krashen is a linguist, educational researcher, and activist.

Currently professor emeritus at the University of Southern California, Krashen has published more than 350 papers and books, contributing to the fields of second language acquisition (SLA), bilingual education, and reading.

He is credited with introducing various influential concepts and terms in the study of second language acquisition, including the Acquisition-Learning hypothesis, the Input hypothesis, Monitor hypothesis, the Affective Filter hypothesis, and the Natural Order hypothesis. which form part of his theory of second language acquisition.

Most recently, Krashen promotes the use of free voluntary reading during second language acquisition, of which he says "I believe that it is the most powerful tool we have in language education, first and second."