Richard Castle is widely regarded as one of the most important architects in eighteenth-century Ireland, yet this is the first book devoted to both Castle’s personal history and his professional career. The study builds on a wealth of information concerning his background. It investigates Castle’s Dutch and Sephardic ancestors, his father’s position at the Polish court, the military career of his siblings in the Saxon/Polish army, his wife’s Huguenot family, and his kinship with English economist David Ricardo. Making use of extensive research data, the book refutes commonly held misconceptions about Castle’s name, family, nationality and religion. This book will be of interest to architectural historians, readers interested in Irish/European cultural studies, and researchers into the Jewish diaspora and into early modern Europe in general.