Katharina Lodders is Research Professor in the Department of Earth & Planetary Sciences at Washington University in St. Louis, MO, USA. She is senior author with Dr. Fegley of The Planetary Scientist's Companion (Oxford University Press, 1998) and the author (or co-author) of over 80 refereed publications in scientific journals and books. Her experimental and theoretical research focuses on topics in cosmochemistry, planetary science, and astronomy. Bruce Fegley, Jr., is Professor of Planetary Sciences in the Department of Earth & Planetary Sciences at Washington University in St. Louis, MO, USA. He is junior author with Dr. Lodders of The Planetary Scientist's Companion (Oxford University Press, 1998) and is senior author of Practical Chemical Thermodynamics for Geoscientists (Academic-Elsevier, scheduled for 2008) with Ms. Rose Osborne. He is the author (or co-author) of over 120 refereed publications in scientific journals and books. At present and over the past 16 years he has taught several advanced undergraduate and graduate level courses in geochemistry and planetary science including "Thermodynamics and Phase Equilibria," "Planetary Geochemistry," and "Earth System Science." Dr.Fegley received his S.B. in Chemistry and PhD. in Geochemistry at MIT and has 25 years of experience in geochemistry, cosmochemistry and planetary science.