This book explores the different aspects of Henry van de Velde's creative activity through a study of his writings and major works of his German period (1900-1916), including his unpublished manuscript on ornament. The study casts light on this major figure in Early Modern architecture, specifically on his aesthetic theory, centered around themes such as "rational conception" and "empathy".This study focuses on this specific period of van de Velde's work, as it constitutes the period of his greatest activity as a designer, teacher, and architect. While examining the relation between his writings and his built works, it thematically addresses the different architectural works realized by the architect during this period.