Jon Kabat-Zinn has played a pivotal role in building the bridge between Buddhist practices of meditation in the East and the Western approach to psychology. We can now receive meditation as a medical treatment thanks to this bridge.
This is probably the most accessible book he has written, while also expressing beautifully the depth of his experience. It is perfect for the beginner and includes a set of guided meditations recorded by the author.
He starts by defining mindfulness very precisely:
Mindfulness is awareness, cultivated by paying attention in a sustained and particular way: on purpose, in the present moment, and non-judgementally.