This document provides a critical review of Krashen's Input Hypothesis, which is one of the five hypotheses that make up Krashen's Monitor Model of second language acquisition. The review examines three major criticisms of the Input Hypothesis. First, it argues that the constructs of "comprehensible input" and "the next level" are vaguely defined, making the hypothesis difficult to test. Second, it asserts that the hypothesis oversimplifies the nature of input. Third, it claims that Krashen made overly broad claims about the explanatory power of the hypothesis without sufficient evidence.