Situated within the historical and current state of writing and adolescent literacy research, this systematic literature review screened 3504 articles to determine the prevalent themes in current research on writing tasks in content-area classrooms. Each of the 3504 studies was evaluated and coded using seven methodological quality indicators. The qualitative synthesis of studies is organized by the overarching categories of context, cognition, and content. The studies are further grouped by relevant themes to explore how the incorporation of writing tasks into content-area instruction benefits the secondary students' content-area learning and knowledge acquisition. Primary themes include the elements of explicit strategy and inquiry-based instruction, the impact of prewriting models, the role of metacognition and journaling, and the writing-related implications for content-area assessment. Recommendations for future research are offered. Additionally, practical implications for secondary content-area teachers are presented.