An overview of research topics and findings from an interdisciplinary, programmatic line of research on writing over the past 25 years is presented. The cross-sectional assessment studies (grades 1 to 9) showed which measures uniquely explained variance in handwriting, spelling, and composing and thus validated their use in assessment. These and the longitudinal studies (grades 1 to 5 and 3 to 7) contributed to knowledge of the cognitive processes of writing, within a working memory architecture that orchestrates multiple component processes in time to achieve specific writing goals, especially the translation of ideas into words, syntax, and text, and transcription (handwriting and spelling) by pen and by keyboard. Combined brain imaging and behavioral studies of writing have provided converging evidence for brain-behavior relationships for handwriting, spelling, and composing and for the role of temporally coordinated working memory, including an orthographic loop with a graphic-motor envelope for word production. A series of instructional studies for at-risk writers, which was taught to all levels of language to overcome working memory inefficiencies, were organized according to the developmental steppingstones in writing acquisition and show that writing problems can be prevented. Other studies with older, struggling writers validated effective instructional approaches for helping struggling writers become reading-writers who integrate both written language skills in literacy learning.