Theory groups and other researchers interested in the systematic prediction of OH stretching wavenumbers for monohydrates were alerted about this blind challenge via news groups, conferences, and direct contact, together with the training set of 10 organic solvates. They were given the possibility to register for the challenge, to be alerted immediately upon the start of the actual competition with the announcement of the test set. Registrations up to the submission deadline are accepted. A unique entry code is provided to each participant in order to allow them later to review their own submitted data.