Answer:
There are many books suitable for beginners that teach about zazen. Understand that zazen is a practice. The best way to learn about zazen is to do it--not just to read about it. From that perspective, the best book for beginners that teaches not only some of the theory behind Zen Buddhism but also clearly instructs how to begin a zazen practice at home is still Philip Kapleau's THE THREE PILLARS OF ZEN.
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