Madonna's doing it. Britney's doing it. And a host of other celebrities are doing it.

They're studying Kabbalah.

Delving into Jewish mysticism brought warnings from scholars: Kabbalah is complex and only for the spiritually mature. But with celebrities like Demi Moore and Gwyneth Paltrow flocking to Kabbalah centers and sporting red-string bracelets as a sign of their newfound interest, the question is a natural: What is Kabbalah?

Traditionally the study of Kabbalah has been reserved for the most learned and pious, not the masses. Jews could not even begin studying it until they were 40 years old.

"There is no simple definition of Kabbalah," says Elliot Wolfson, professor of Hebrew and Judaic studies at New York University and a leading scholar of Kabbalah. "The word means 'tradition,' and from some time in the Middle Ages, the term began to be used to refer to secrets about the divine nature, the cosmos and the human soul or, principally, the soul of the Jew.

"Kabbalah relates both to esoteric wisdom and contemplative practices that facilitate communion and sometimes even union of the individual and God."

Kabbalah literally means "reception," which is synonymous with the word "tradition" in Hebrew, says professor Hava Tirosh-Samuelson of Arizona State University, who studies the relationship between philosophy and Kabbalah. It refers to receiving the inner, hidden or esoteric meaning of divine revelation, she says.

It is closely aligned with the traditional, Orthodox form of Judaism, says Pinchas Giller, professor of Jewish thought at the University of Judaism in Bel-Air, Calif., and an expert in Kabbalah.

"There are meditative and magical practices, but the main application is to provide a layer of deeper meaning for observing the traditional Jewish commandments," he says.

Practices include special focus, when reciting prayers, on colors that correspond to specific potencies of the divine, Wolfson says

The teachings of Kabbalah go back 2,000 years and were orally transmitted, Giller says.

"It became a written tradition in the late 12th century and flourished in the 13th century in Spain," Tirosh-Samuelson says. "Several Kabbalistic schools developed concurrently, but the most influential one was the school that produced the magnum opus of Kabbalah, Sefer ha-Zohar (The Book of Enlightenment)."

The Zohar can be described as a mystical commentary on many sections of the Torah, or first five books of the Hebrew Bible. It deals with five theological issues, says Jim Wallis in "The Religion Book": the nature of God, the creation of the Universe, the destiny of humanity, the nature of evil and the meaning of the Bible.

To study Kabbalah means primarily to study the Zohar, Tirosh-Samuelson says.

"Torah deals with the physical and with this world," says Rabbi Mendy Wineberg of Chabad House Center in Overland Park, Kan. "It does not generally discuss things that don't apply to our daily service of God in the here and now. Kabbalah, on the other hand, looks at the spiritual reasons and outcomes of our actions.

"Torah is called the 'body,' and Kabbalah is called the 'soul'. Kabbalah also teaches us about God and creation as well as our souls and our connection to God. By learning about our spiritual side we can affect our physical side."

The current flourishing of Kabbalah has little to do with the tradition, but rather reflects the needs of spiritual seekers today, both Jews and non-Jews, Tirosh-Samuelson says. She sees three reasons for Kabbalah's present popularity:

* It consists of a strong psychological emphasis, since it concerns the pursuit of perfection, and with the spiritual transformation of the individual.

* It is highly visual and employs the power of the imaginative. Its teachings can be viewed as a kind of Jewish art, which takes place not in space, but in the mind of the person who practices Kabbalah.

* It has much to say about sexuality, both human and divine.

"The combination of the emotional, the imaginative and the sexual makes Kabbalah extremely attractive to artists, who are seeking new imagery or who are displeased with the shallowness and emptiness of American consumerist culture," she says.

Jewish scholars express strong feelings about the spotlight on Kabbalah that is reflected from the celebrities. Numerous reports express concern about what they see as distortions of Kabbalah. A California rabbi blasted the Kabbalah Centre in Los Angeles for allowing Madonna to become its "principal spokesperson."

In an article on its Web site, the Bnei Baruch World Center for Kabbalah Studies says: "Today, many well-known celebrities have popularized a New Age pop-psychology distortion of Kabbalah that has more in common with the writings of Deepak Chopra than with any authentic Jewish source."

Many traditional Jewish stories from the Talmud and other sources even discourage the pursuit of mystical experiences "as dangerous and irresponsible," according to the Bnei Baruch article.

Tirosh-Samuelson says she believes Kabbalah's popularity is based on reinterpretation of Jewish mysticism for today but also on misinterpretation of the tradition.

"The main danger in the popularization of Kabbalah is the belief that it has nothing to do with traditional Judaism or that one does not need to live as a Jew in order to engage in Kabbalah," she says. "Kabbalah is an integral part of Judaism and cannot and should not be wrested from its Jewish moorings."

Wolfson thinks Madonna and other celebrities have been misled. "I suspect the celebrities are attracted because of the emptiness of American materialism," he says. A repackaged Kabbalah is treated "as if it is a spiritual quick-fix. It is demeaning and does not honor the complexity of the tradition. It is like a sixth-grade teacher trying to make Einstein's theory of general relativity understandable to his or her students."

Rabbi David Fine of Congregation Beth Israel Abraham & Voliner, an Orthodox synagogue in Overland Park, says the popular version "has nothing to do with genuine Kabbalah." Jumping right into a study of Kabbalah "would be like trying to study advanced calculus without knowing basic arithmetic," he says. "Kabbalah is part of a very traditional and conservative system.

"There are very strict guidelines to practicing Kabbalah, and very few people in the world today actually practice Kabbalah as it was traditionally practiced, although many study it. It is very demanding, and it requires a purity of soul and personality that Madonna just doesn't have."

This interest in "pseudo-Kabbalah" "dumbs down" Kabbalah until it is no longer recognizable, Fine says. But he concedes it has raised awareness, among both Jews and non-Jews, of traditional Judaism and certain Jewish practices.

Giller also doesn't see the attention as all bad.

"Every time in Jewish history that outbreaks of Judeaophilia have occurred, the Jews have gratefully accepted a few crumbs of positive attention," he says.

But he sees what is happening as indicative of what has gone on within Judaism since the end of World War II. He says Jews have been preoccupied with their role in history and with Israel and the Holocaust, and they have neglected "the traditional emphasis of Judaism, which includes an interest in God, the soul and spiritual practice."

"So in many ways," Giller says, "there is an eruption of interest in overtly spiritual things, to which the synagogue world and mainstream Jewish institutions are not always prepared to respond."

Kabbalah has always been a crossover phenomenon, with kabbalists teaching gentiles in the third, 12th, 16th and 18th centuries, he says.

"So scholars shouldn't be surprised when it happens again," he says. "People can't choose their relatives, and scholars can't dictate the history of their chosen fields. However, being nearby during this present-day eruption of interest is good for me. I prefer living traditions."

But to Wolfson, what is being offered today is not the tradition but a distorted "pop version that is far more a form of New Age occult astrology and magic than a genuine expression of Kabbalah."

Madonna performs at Madison Square Garden June 16. The red thread on her wrist is an indication that the Material Girl has been delving into the decidedly spiritual realm of Kabbalah. Actor Ashton Kutcher speaks at the "Family Fun Day" in March at the Kabbalah Centre in Los Angeles.