It’s Earth Day, the 39th Earth Day to be exact, and a good day to think about where books come from. The relationship between trees and reading has inspired an intriguing website, Eco-Libris, and a green mission. The Eco-Libris folks encourage us to plant a tree for each and every book we read. This makes reading a truly sustainable endeavor. How do they do it? Visit Eco-Libris and find out.