Despite the preponderance of research on extensive reading (ER), the research field still suffers from a lack of common understanding of what ER is and how it should be implemented. From the perspective of Day and Bamford's (2002) seminal ten principles for teaching ER, the present methodological synthesis aimed to systematically review and critically appraise the reporting practice of how previous studies implemented ER. A total of 72 primary studies were retrieved and reviewed. The findings suggested that many studies did not explicitly report ER characteristics in their articles, making it difficult to understand how ER was operationalized and practiced. Suggestions for future studies are discussed.