Publisher Summary This chapter discusses important factors controlling the performance of activated carbon adsorption during drinking water treatment. The micropore size distribution and volume of activated carbons are important for the adsorption of several small molecular weight organic contaminants. Depending on the dimensions of a molecule, there is an optimum micropore size region that maximizes its adsorption because of enhanced adsorption in these regions, the presence of dissolved natural organic matter (DOM) in natural waters, and its impact on target compound adsorption is unavoidable. Studies are needed to examine the optimum pore region for the adsorption of various synthetic organic chemicals (SOCs) in the presence of different DOMs. Water molecules bound to carbon surfaces can significantly hinder SOC adsorption. Activated carbons have hydrophobic surfaces with low affinity toward water. The use of oxidants prior to activated carbon decreases the effectiveness of activated carbons for target compounds.