ABSTRACT The article briefly summarizes and then discusses Krashen's Input Hypothesis as presented in his Principles and Practice in Second Language Acquisition. The Input Hypothesis is considered both as a psycholinguistic and as a pedagogical model. I suggest that as a psycho-linguistic model the Input Hypothesis fails to account convincingly for the widely accepted fact of fossilization (arrested L2 acquisition) in an acquisition-rich environment. As a pedagogical model the Input Hypothesis may not be directly applicable to the reality of the U.S. high school or university foreign language classes, since these are so far removed from the immersion/second language environments on which much of the theory underlying the model is based.