A recent editor of Robert Fludd describes him as “the most prominent Renaissance Christian Neoplatonist alchemist of his time, and the greatest summarizer and synthesizer of that tradition of his age” (Huffman 13). To these accolades may be added his successful practice of medicine in London – which, despite sharp attacks on Aristotle and Galen, eventually resulted in Fludd's admission to the Royal College of Physicians – and his championing of the Rosicrucians. He was attacked by such giants of the New Philosophy as Kepler, Mersenne, and Gassendi; however, William Harvey and William Gilbert were influential friends. Fludd published extensively but appears to have attracted greatest interest on the Continent; he is best known today for his extraordinarily detailed study of interrelationships between the macrocosm and microcosm, the Utriusque cosmi maioris scilicet et minoris, metaphysica, physica atque technica historia, which directly reflects his religious and philosophical views and, accompanied by its exquisitely detailed engravings, first issued from the de Bry press in Oppenheim in 1617.

A sense of the range of Fludd's thought (with its frequent links to Paracelsus and the Neoplatonists) may be gained from his Mosaicall Philosophy, first published posthumously in Latin in 1638. Here may be noted, for example, his beliefs in the indebtedness of pagan philosophy to the writings of Moses; the Holy Spirit as the origin of all creation, which has its basis in the three “mosaic” principles of light, darkness, and a complex entity known as the “waters”; the world soul or anima mundi; man as microcosm; the doctrine of sympathies and antipathies; and the “magnetical” operation of the notorious cure known as the Weapon Salve.