"He's such a spokesman for freedom and transcendence that people have found him to be a great literary voice for centuries," says Carl Ernst, head of religious studies at the University of North Carolina at Chapel Hill.
Some scholars compare Rumi's revival to similar fads, such as the burst of interest in Kahlil Gibran's poetry a generation ago.
But Mr. Ernst believes the Rumi phenomenon is bigger.
The mystic's current fans range from Islamic scholars to New Age enthusiasts. Barks says he can't explain the phenomenon.
Bly says Rumi fills a place in the Christian tradition left vacant when the Gnostics - Christian mystics - were discredited as heretics by early Christian religious leaders. That ecstatic impulse has occasionally re-emerged with St. Francis and some of the medieval mystics, such as St. Teresa. The late 20th century is seeing a revival of the Pentacostal, charismatic movement in the US. But the mystical tradition never blossomed in mainstream Christianity to the extent that it has in the Muslims' Sufi tradition.
Rumi was also a rebel of sorts in his day. His poetry, which in the original Persian is densely rhymed and rhythmed, breaks many of the rules of classical poetry. It sometimes runs too long, sometimes too short. His images are playful, full of the richness and abandon of childhood. He compares himself to a magician, creates images the way a wizard makes birds appear from the palm of his hand.
"He doesn't try to describe mystical love, he tries to linguistically show it to us," says Fatemeh Keshavarz, professor of Persian language and literature at Washington University in St. Louis. "He mirrors his experience of mystical love."
In the Muslim world, many consider Rumi a saint.
"My experience of a poet-saint is that they affect the deepest regions of one's intelligence and heart," says Daniel Ladinsky, a South Carolina poet who works with translations of Shams-ud-Din Muhammad Hafiz, a 14th-century Sufi poet who is also enjoying a revival in America.
Mr. Ladinsky learned about the Persian mystical poets while living in a monastic community of sorts in India. He says both Rumi and Hafiz address his "profound need to make sense out of God.... I simply want to get along with the One I have to live with."
Addie Wolbach, a mother of three who lives in Boston, began reading the Persian mystics 10 years ago.