Miracle of Mindfulness (Thich Nhat Hanh )
Thich Nhat Hanh (1926–2022) was a Vietnamese Buddhist Zen Master, poet, and peace activist. He is by all accounts a grandfather of mindfulness and one of the most prolific authors on the subject.
If you want to understand mindfulness in its purest form, this is the place to start.
Interestingly, the Miracle Of Mindfulness was developed out of a long letter from Thich Nhat Hanh to a fellow Buddhist monk in Vietnam in the midst of the war in 1975. Little did he know that letter would change so many lives.
Some say it is the best book on mindfulness meditation, and it certainly is a contender.