The patient sat with his eyes closed, submerged in the rhythm of his own breathing, and after a while noticed that he was thinking about his troubled relationship with his father.

“I was able to be there, present for the pain,” he said, when the meditation session ended. “To just let it be what it was, without thinking it through.”

The therapist nodded.

“Acceptance is what it was,” he continued. “Just letting it be. Not trying to change anything.”

“That’s it,” the therapist said. “That’s it, and that’s big.”

This exercise in focused awareness and mental catch-and-release of emotions has become perhaps the most popular new psychotherapy technique of the past decade. Mindfulness meditation, as it is called, is rooted in the teachings of a fifth-century B.C. Indian prince, Siddhartha Gautama, later known as the Buddha. It is catching the attention of talk therapists of all stripes, including academic researchers, Freudian analysts in private practice and skeptics who see all the hallmarks of another fad.