The Input Hypothesis, proposed by linguist Stephen Krashen, suggests that language acquisition occurs when learners are exposed to language input that is slightly above their current proficiency level, referred to as i+1. This means that learners should understand most of the input but still encounter new vocabulary and structures that challenge them. According to the Input Hypothesis, comprehensible input is essential for effective language learning. When learners receive this type of input, they can naturally acquire the language without explicit instruction. This theory emphasizes the importance of exposure to meaningful language in context, rather than focusing solely on grammar rules or vocabulary lists.