Energy is typically regarded as understandable despite its multiple forms of storage and transfer. Yet entropy is an enigma, in part because of the common view that it represents disorder.

Harvey S. Leff is Professor Emeritus of Physics at California State Polytechnic University in Pomona, California and Visiting Scholar at Reed College in Portland, Oregon. He has published widely in thermal physics, writing primarily for physics and chemistry teachers and students. With Andrew Rex, Leff co-edited Maxwell's Demon 2: Entropy, Classical and Quantum Information, Computing. He served as President of the American Association of Physics Teachers, and is a Fellow of the American Physical Society and the American Association of Physics Teachers, and a Consulting Editor for the American Journal of Physics. When not doing physics, Leff plays drums in two bands, The Leff Trio and Jazz Up, and he is the former drummer in The Out-Laws of Physics.

1 Energy is Universal. 2 Energy is Not Enough. 3 Entropy: Energy's Needed Partner. 4 Gases, Solids, Polymers. 5 Radiatin and Photons. 6 Numerical Entropy. 7 Language and Philosophy of Thermodynamics. 8 Working, Heating, Cooling. 9 Sanctity of the 2nd law of Thermodynamics. 10 Reflections and Extensions. 11 Appendices: Mathematical Identities