The reaction of an organo-chloro- or organo-alkoxy-silane with a compound containing a reactive group. In liquid chromatography, it refers to the process of derivatizing the solute before chromatography in order to make it detectable or to prevent unwanted stationary phase interactions. It can also refer to the process of adding a chemically bonded phase to a solid support or to deactivating the packing to cut down on surface activity.