“Mindfulness in Plain English” by Ven. Henepola Gunaratana is a highly regarded, practical and popular introduction to meditation and mindfulness practice.  A free copy can be downloaded here.

“A masterpiece.”—Jon Kabat-Zinn

“A classic—one of the very best English sources for authoritative explanations of mindfulness.” —Daniel Goleman

“Of great value to newcomers… especially people without access to a teacher.”
—Larry Rosenberg, author of Breath by Breath

“Wonderfully clear and straightforward.”
–Joseph Goldstein, author of A Heart Full of Peace

“Pithy and practical.”
–Shambhala Sun

“Jargon-free.”
–USA Today

The book is available to download for free here.  There is an online version, a PDF version, and i-phone version and an e-book reader version as well!