The Hebrew word 'Kabbalah' (קַבָּלָה) means 'reception' or 'tradition.' It refers to secret knowledge passed from teacher to student in an unbroken chain that, the tradition says, goes all the way back to God's revelation at Mount Sinai. The claim is bold. It is not just that Kabbalah holds ancient wisdom. It is that the hidden, inner meaning of the Torah was handed to Moses along with the public law, and that this inner teaching was kept alive and developed for three thousand years by an unbroken line of teachers and students. You cannot prove that claim the way the tradition tells it. What you can prove is this: Jewish mystics produced some of the most careful and far-reaching writing about God in the history of religion, and the tradition took formal shape in medieval Provence and Spain. Its greatest work, the Zohar, was written in thirteenth-century Castile.
Kabbalah grew in clear stages. The first was Merkabah ('chariot') mysticism, from the first to seventh centuries CE. It produced the 'Hekhalot' texts, accounts of trained practitioners rising through seven heavenly palaces to the throne of God, under strict conditions. Next came the Sefer Yetzirah ('Book of Formation'), written somewhere between the third and sixth centuries CE. It introduced the 32 Paths of Wisdom (the 10 Sephiroth plus the 22 letters) and the idea that God made the world through the Hebrew alphabet, the letters as the raw building blocks of reality. In twelfth-century Provence, small proto-Kabbalistic groups appeared, along with the Sefer ha-Bahir ('Book of Illumination') and the first organized treatment of the Sephiroth as a system of divine qualities. Then came the Zohar. Tradition credits it to the second-century rabbi Shimon bar Yochai, but it was almost certainly written by the thirteenth-century Castilian scholar Moses de León. It completed the classic shape of Kabbalah.
From the thirteenth through the sixteenth centuries, classical Kabbalah split into three schools that still matter today. The Theosophical Kabbalah, built around the Zohar and developed in Castile, tries to understand the inner life of God and the structure of the divine world. It is more a mystical theology than a how-to manual, but it lays the groundwork everything else builds on. The Prophetic or Ecstatic Kabbalah of Abraham Abulafia (1240-1291), which grew up at the same time in Spain and Italy, is all about method: combining and rearranging Hebrew letters, controlled breathing, and specific postures, all aimed at an ecstatic union with the divine mind. The Practical Kabbalah, which came later, puts the knowledge to magical use: making amulets, using divine names for protection and healing, and rituals meant to influence the divine world.
Non-Jews began adopting Kabbalah during the Renaissance, and they spelled it differently, 'Qabalah,' to mark the difference from the Jewish original. Giovanni Pico della Mirandola (1463-1494) and Johannes Reuchlin (1455-1522) argued that Kabbalah was the strongest proof of Christian theology around, because it seemed to show, from Jewish sources, that Jesus was divine and the Trinity was true. Later thinkers, including Heinrich Cornelius Agrippa, John Dee, and Robert Fludd, grew this 'Christian Kabbalah' into a full Hermetic system that mixed Kabbalah with Neoplatonism, astrology, alchemy, and ceremonial magic. In the nineteenth century, the Hermetic Order of the Golden Dawn, through Mathers, Westcott, and later Aleister Crowley and Dion Fortune, turned the Hermetic Qabalah into the organized magical framework that most modern Western occultism still rests on. The two streams, Jewish Kabbalah and Hermetic Qabalah, share the Tree of Life but differ a lot in their theology, their practice, and what they are for.