  In this 2nd chapter of the book Quantum Mechanical Prediction of
Thermochemical Data" (ed. Jerzy Cioslowski, Kluwer, 2001; ISBN 0-7923-7077-5),
we review the nonempirical computational thermochemistry methods W1 and W2
theory and their variants. The chapter is made available online following a
change in publisher E-print policy.
