The surface properties of activated carbons (AC) play a significant role when these materials are used for adsorption from liquid phases or as supports For catalysts. Different ways to describe the chemistry of carbon surfaces are considered: (1) according to the concept of chemical groups as developed in organic chemistry (XPS of AC is illustrated by nitrogen functions); (ii) by active surface area and polar surface area. No single method is able to give a quantitative description of the surface chemistry of a carbon material.