There has been an increasing professional and policy interest in using formative assessment as part of the learning process in the classroom, with increasing numbers of educators regarding it as an effective means of closing the gap between students' current and desired performance. However, there is a range of different views on what actually constitutes formative assessment and how it may be incorporated into regular classroom teaching. Furthermore, formative assessment is often misconstrued in reality, and teachers face considerable challenges in implementing formative assessment in their daily classes, particularly in the ESL teaching context. The purpose of this article is, therefore, to review how formative assessment has recently been discussed in both general education and L2 assessment fields, and to illustrate how formative assessment can be implemented in task-based language teaching in the daily ESL classroom.