The Anapanasati Sutta teaches the sixteen steps the Buddha followed to develop the mindfulness that led to his enlightenment. It is well-known to Theravada monks and nuns (to use a Western term that doesn’t really fit; these “monks and nuns” worship no one), but not to the ordinary people who live in the Theravada countries including Sri Lanka, Burma, Thailand, Laos, Cambodia, and the Viet Nam/Cambodian border area.
Rinzai Zen and its traditions of koans is equally well-known to the “monks and nuns” of China, Japan, Korea, and most of Viet Nam, but the practices are not well-known to lay people.
Such a bizarre circumstance! The Theravada school knows how to penetrate Zen koans but never tries! I have spoken with only three Theravada monks and one nun in person, asking them if they had ever tried to penetrate a Zen koan, and each of them told me: “We don’t do that.” Why not? “We are not Zen practitioners.”
The Rinzai Zen school tries to penetrate koans, but knows nothing about Theravada mindfulness! When I ask Rinzai Zen teachers: “Why don’t you teach Theravada mindfulness to your students?” they reply: “We are not Theravada practitioners.”
So nowadays I spend a little time every day, making contact with Theravada and Rinzai Zen teachers, urging the former to teach their students to apply their mindfulness to koans and asking the latter to teach their students Theravada mindfulness so that they can develop the mindfulness needed to penetrate koans.
If this quixotic quest succeeds, the walls between these two schools will come down. If a Theravada teacher teaches his or her students to tackle koans with their mindfulness, and if a Rinzai Zen teacher teaches his or her students how to develop mindfulness by following the steps of the Anapanasati Sutta and to apply that mindfulness to koan study, then both teachers are teaching the very same thing and the labels “Theravada teacher” and “Rinzai Zen” teacher will no longer apply.
A few Soto teachers use koans as well…
How To Practice Zen 