This paper presents an overview of what has come to be known as the Interaction Hypothesis, the basic tenet of which is that through input and interaction with interlocutors, language learners have opportunities to notice differences between their own formulations of the target language and the language of their conversational partners. They also receive feedback which both modifies the linguistic input they receive and pushes them to modify their output during conversation. This paper focuses on the major constructs of this approach to SLA, namely, input, interaction, feedback and output, and discusses recent literature that addresses these issues.