Although astrologers and astrological concepts were instrumental in formulating the core assumptions of the modern New Age movement in the late 19th and early 20th centuries, the increasing number of scholarly studies of the New Age movement pay almost no attention to astrology. The only two English language histories of modern astrology set out the role of the English astrologer Alan Leo (1860-1917) in creating an astrology designed to facilitate spiritual evolution and the coming of the New Age. This paper examines the foundation of an astrology of spiritual development and psychological growth in the USA and examines the key role played by Marc Edmund Jones (1888-1980). Jones used arguments based on the history of astrology, strongly influenced by theosophical theories of history, to justify his reform of astrology.