Sir Jonas Moore (1617-79) - practical mathematician, teacher, author, surveyor, cartographer, Ordnance Officer, courtier and patron of astronomy - enjoyed a remarkable career by the standards of any age, and was one of the first to make a substantial fortune from mathematical practice. In the course of his 'rise' (as his friend John Aubrey termed it) from humble origins in Lancashire to a knighthood, membership of the Royal Society and favour at the court of Charles II, he participated in the two most ambitious projects of the age: the draining of the Great Level of the Fens (under the Dutch engineer Sir Cornelius Vermuyden) and the building of a massive harbour wall, the Mole, at Tangier. In later life his wealth and influence as Surveyor-General of the Ordnance enabled him to become a patron of the new Royal Observatory at Greenwich. This biography, the first detailed study of Moore, examines his career in the context of changing views of mathematics, especially in relation to 17th-century disputes about the proper nature of the discipline and its effectiveness as means of solving practical problems. It sheds light on the roles played by patrons and teachers of the subject, most notably the figurehead of English mathematicians, William Oughtred. It also illuminates the confidence in practical mathematics that inspired Moore's unique activities as a patron, and the uneasy relationship between this and the natural-philosophical concerns of the early Royal Society. This wide-ranging study challenges the current conventionally narrow view of mathematics in the time of the 17th-century 'scientific revolution'.