The term “occultism” was first used in the first half of the nineteenth century, but has its roots in a much older history. The adjective occultus (Lat., “hidden”), from which it derived, was used to indicate beliefs, ideas, and practices related to forces or properties of nature that were considered to be impenetrable to the normal human senses, but very real and powerful all the same. In popularizing the term “occultism,” nineteenth century authors aimed at a new systematization of this body of esoteric knowledge, to which they also added some new, modern elements. The term has been increasingly used by specialists to indicate a specific historical current in the history of Western esotericism, starting in the second half of the nineteenth century and going well into the twentieth. ⸙The term “occultism” has been defined in a variety of ways since its first appearance in France (as occultisme), in the first half of the nineteenth century. The earliest occurrence appears to be in a “dictionary of new words” by Jean-Baptiste Richard, Enrichissement de la langue française (1842), but it was thanks to the pen of Eliphas Lévi (ps. of Alphonse-Louis Constant, 1810‒1875) that the term became increasingly popular from the 1850s onwards. Later, and mostly under the influence of Lévi’s writings, the term passed into other languages. In English, it was probably introduced by Helena Petrovna Blavatsky (1831‒1861) in one of her earliest articles, published in an American spiritualist journal. Despite being relatively recent, the term “occultism” was derived from the adjective occultus (Lat., “hidden”), which has a much older history. In this respect, as it has often been remarked, the history of the term presents similarities with that of the related noun “esotericism,” whose first occurrence can be found in Germany in the late eighteenth century (in the form Esoterik) as a derivative of the much older adjective “esoteric” (Neugebauer-Wölk 2010). In the case of occultism, the immediate reference was to sets of doctrines, beliefs, and practices that had been defined, especially since the Renaissance, with expressions such as “occult philosophy” and “occult sciences” — magic, astrology, alchemy, and Kabbalah being the most commonly included in this category (Hanegraaff 2013). The object of these disciplines was understood to be the study and the use of those properties of nature that had been traditionally defined, since late Antiquity and throughout the Middle Ages, as “occult” (qualitates occultae), because they were considered to be impenetrable to the normal human senses, but still very real and effective. In the context of the neo-Platonic and Hermetic revival of the Renaissance, influential authors such as Marsilio Ficino (1433‒1499), Giovanni Pico della Mirandola (1463‒1494), and Paracelsus (ps. of Theophrastus Bombastus von Hohenheim, 1493‒1541) devoted significant space to a description and a theorization of these occult properties. Heinrich Cornelius Agrippa (1486‒1535) on the other hand, with his De Occulta Philosophia (1533), can be seen as one of the earliest authors who tried to systematize this body of doctrines into a coherent whole and under a comprehensive name. Speculations about “occult properties” were increasingly challenged during the Scientific Revolution and the period of the Enlightenment, but it is not entirely correct to say that they were simply rejected. In some cases, such as electricity and magnetism, there were efforts at reinterpreting them within new scientific theories, focusing less on the ultimate causes than on the regularity of their behavior and their empirically verifiable effects. But whereas it was theoretically possible to create new interpretive frameworks for particular natural phenomena that had been earlier considered as mysterious and inexplicable, it was much more problematic to accept the idea of a specific branch of knowledge such as “occult philosophy,” or “magic,” which would be based on the systematic theorization and use of forces that science could not verify, explain, or even identify. In creating and popularizing “occultism” in the nineteenth century, authors such as Lévi and his later emulators were reacting against what they perceived as the excesses of the Enlightenment and the materialist drift of contemporary science (Webb 1974; Laurant 1993). In this sense, they clearly aimed at a reorganization and a new systematization of this body of doctrines that had been increasingly marginalized since the seventeenth century. At the same time, this attempt at a new synthesis added new elements to the traditional framework of Renaissance philosophia occulta. To mention but two of the most significant examples, currents such as Swedenborgianism and Mesmerism were particularly influential, especially in the earliest phase of occultism. They offered to the occultists a wealth of ideas concerning, on the one hand, the otherworld and the destiny of man after death, and, on the other, the theorization of a vital force permeating both nature and the human body together with new conceptual paradigms of human personality. Other new elements included the popularization of the Tarot cards as a symbolic system and, for some authors, the influence of concepts and practices derived from Eastern religious traditions (especially, albeit not exclusively, from India).