The Philadelphia architect and master builder Owen Biddle (1774–1806) contributed to the making of some of the early Republic's most important buildings and is best known as the author of one of the first American-authored architectural books. During the course of his relatively brief career, Biddle's achievements in architecture and theory were profoundly shaped by Philadelphia's distinctive, Quaker-influenced economic and artistic culture. Focusing on two hitherto unknown row houses built by Biddle between 1798 and 1801, Conor Lucey reveals for the first time the business and property interests of this important if enigmatic figure. Viewing Biddle's work against the socioeconomic backdrop of Federal-era Philadelphia, and drawing on previously unexplored archival material, Owen Biddle and Philadelphia's Real Estate Market, 1798–1806 situates Biddle's real estate ventures within the context of the city's early nineteenth-century building world. This study of Biddle's career as builder-developer expands our knowledge of his professional life and our understanding of the formation of his ideas.