Mesoporous silica (MS) has been one of the most versatile and successful adsorbents for the removal of environmental pollutants in recent years. The extent to which its structural properties can be tailored and the ease with which such morphological properties can be manipulated are widely acknowledged as major advantages of MS over other adsorbents. In addition to this, modifications to the surface of MS have also been explored in recent years. When the morphology and surface functionality of adsorbents are optimised, great improvements in selective adsorption capacities for a wide range of different pollutant types have been achieved. This review article will explore the most common functional groups deposited at adsorbent surfaces, and the reagents and methods used to deposit these groups to the MS surface, for the purpose of increasing the adsorption capacity and/or selectivity for both inorganic and organic wastewater pollutants. A selection of successful surface functionalizations which have been performed on different substrates will also be outlined, to guide future MS surface modifications.