Zen Mind, Beginner's Mind by Shunru Suzuki. I first encountered it when I was around 19, and came back to it at various points. At around age 55 I finally start

Zen Mind, Beginner's Mind by Shunru Suzuki. I first encountered it when I was around 19, and came back to it at various points. At around age 55 I finally started a serious Zen practice which involves an hour a day of meditation, working on koans with a Zen teacher, and more. I've been doing that for around 10 years. It has truly been life-altering in the deepest possible way. I've read other Zen books but that one by Suzuki is the one that started everything and it still holds a unique and very valuable place.