The fundamentals of aqueous solubility, and the factors that affect it, are briefly outlined, followed by a short introduction to quantitative structure-property relationships. Early (pre-1990) work on aqueous solubility prediction is summarised, and a more detailed presentation and critical discussion are given of the results of most, if not all, of those published in silico prediction studies from 1990 onwards that have used diverse training sets. A table is presented of a number of studies that have used a 21-compound test set of drugs and pesticides to validate their aqueous solubility models. Finally, the results are given of a test of 15 commercially available software programs for aqueous solubility prediction, using a test set of 122 drugs with accurately measured aqueous solubilities.