This introductory engineering textbook on heat and mass transfer, written by John H. Lienhard IV, Professor at University of Houston and John H. Lienhard IV, Professor at Massachusetts Institute of Technology is now available online without charge. One aim of this project is to "explore the possibilities of placing textbooks online." The idea is that the online format holds two key benefits -- ease of continuous updates or corrections, and the "potential for fundamentally altering the economics of higher education, particularly those in environments where money is scarce." To these ends, the website also posts a history of the various versions and statistics on downloads of the book worldwide.