When Robert Pirsig's Zen and the Art of Motorcycle Maintenance was first published in 1974, it caused a literary sensation. An entire generation was profoundly affected by the story of the narrator, his son, Chris, and their month-long motorcycle odyssey from Minnesota to California. A combination of philosophical speculation and psychological tension, the book is a complex story of relationships, values, madness, and, eventually, enlightenment.

Ron Di Santo and Tom Steele have spent years investigating the background and underlying symbolism of Pirsig's work. Together, and...