The Hansen solubility parameter approach is revisited by implementing the thermodynamics of dissolution and mixing. Hansen's pragmatic approach has earned its spurs in predicting solvents for polymer solutions, but for molecular solutes improvements are needed. By going into the details of entropy and enthalpy, several corrections are suggested that make the methodology thermodynamically sound without losing its ease of use. The most important corrections include accounting for the solvent molecules’ size, the destruction of the solid's crystal structure, and the specificity of hydrogen‐bonding interactions, as well as opportunities to predict the solubility at extrapolated temperatures. Testing the original and the improved methods on a large industrial dataset including solvent blends, fit qualities improved from 0.89 to 0.97 and the percentage of correct predictions rose from 54 % to 78 %. Full Matlab scripts are included in the Supporting Information, allowing readers to implement these improvements on their own datasets.

The Cover Feature shows an artist's impression of the challenge of predicting the solubility of agrochemicals, cosmetics and pharmaceuticals. Such predictions often work for polymers, but not for small molecules. By including the thermodyamics of mixing and dissolution, researchers from the University of Amsterdam and the Solvay Lab of the Future in Bordeaux created a set of models that can predict small‐molecule solubility (artwork by Itamar Daube, http://www.itamardaube.com). More information can be found in the Full Paper by M. J. Louwerse et al on page 2999 in Issue 21, 2017 (DOI: 10.1002/cphc.201700408).