The fundamental role played by this book is that it theoretically and experimentally observes and analyses the impact of the implicit and explicit corrective feedback on grammar acquisition of ESL students in their natural learning environment. It does this with the help of relatively separate measurement tests of implicit and explicit knowledge. The book provides empirical, pedagogical and methodological implications which help clarify some of the ambiguities and substantiate some of the findings existing in the literature review of this field of study.