This article discusses five trends in research on writing as a learning activity. Firstly, earlier decades were marked by conflicting views about the effects of writing on learning; in the past decade, the use of meta-analysis has shown that the effects of writing on learning are reliable, and that several variables mediate and moderate these effects. Secondly, in earlier decades, it was thought that text as a medium inherently elicited thinking and learning. Research during the past decade has indicated that writing to learn is a self-regulated activity, dependent on the goals and strategies of the writer. Thirdly, the Writing Across the Curriculum (WAC) movement emphasized domain-general approaches to Writing to Learn (WTL). Much recent research is consistent with the Writing in the Disciplines (WID) movement, incorporating genres that embody forms of reasoning specific to a given discipline. Fourthly, WTL as a classroom practice was always partially social, but the theoretical conceptualization of it was largely individual. During the past two decades, WTL has broadened to include theories and research that integrate social and psychological processes. Fifthly, WTL research has traditionally focused on epistemic learning in schools; more recently, it has been extended to include reflective learning in the professions and additional kinds of outcomes.