Using content analysis, this review study examines 219 empirical research articles published in Assessing Writing (2000–2018) to give a view of the development of writing assessment over the past 25 years. It reports overall and periodic analyses (2000–2009 and 2010–2018) of the contextual, theoretical, and methodological orientations of those articles to gain a comprehensive understanding of what has been assessed in writing and how. Findings indicate that the typical research contexts and participants were L1 undergraduates in U.S. universities/colleges, and the main research foci were validity and reliability, feedback, and testing performance. Among the theoretical orientations from a measurement-theory perspective and a writing-theory perspective, the most common orientations were Generalizability Theory, writing in a sociocultural context, and writing as a cognitive process. Research methodologies were predominately quantitative and text data represented the main source. Periodical analyses show a trend of studies taking place outside North America, covering more macro-contexts, investigating raters, using a combination of methodologies, and drawing on experimental data.