The most remarkable theory which aims to offer an overall explanation for SLA is Krashen's Monitor Theory. As documented by the professional literature, although it has received a great deal of criticism, this theory has had a great influence on all aspect of second language research and teaching since the 1980s. Krashen's theory seems to be attractive to many language teachers all over the world. Based on my experience as an EFL teacher and researcher, I attempt to provide a critical analysis of the theory's five main hypotheses and the applicability of these proposals in foreign language contexts.