One of the best books to comprehensively, accessibly, and without too much esotericism* introduce the reader to the basics of Buddhist meditation and/or mind/heart training. A Theravadin rather down-to-earth approach.
Old version can be found online as a .pdf and .epub – Mindfulness in Plain English
* There is at least one passage, which may make the empirically minded reader raise an eyebrow as the claims do not exactly fit with the existing scientific paradigms, but that is just one passage for the whole book. And the book is very good. And who knows, maybe the author and many other Buddhist writers are right and the current Western paradigm is outdated…