The physicochemical reasons behind the delicate equilibrium established between the adsorbed and the mobile phases are ultimately dictated by the specific interactions between silica surface functionalities and the adsorbate, resulting in different adsorption constants. There are many reasons to report on silica interacting with biomolecules. The most obvious one is that on the Earth's crust, oxygen and silicon are the most abundant atomic species, with percentages of 45.5% and 27.2%, respectively, which manifests itself in a large variety of silica and silicate minerals so that the contact between living matter and these materials is ubiquitous. The adsorption of other molecules, which are not rigorously biomolecules, has also been addressed in section 9, because their behaviors mimic that of residues to be found in real proteins. From the methodological point of view, only methods able to properly handle relatively weak intermolecular interactions should be adopted.