Trace organic compounds such as pesticides and odor-causing compounds are frequent contaminants of drinking water supplies. The removal of these substances by porous adsorbents is complicated by the presence of natural organic matter. Concentrations of NOM are frequently 103 to 106 times larger than those of the trace compounds. The size and molecular characteristics of NOM result in competition for the same adsorption sites as well as pore blockage, and the pore size distribution of the adsorbent determines the type and extent of the competition. Data from studies with controlled pore size adsorbents that show these effects will be presented. If the amount of pore blockage by NOM is small, the quantity of trace compound adsorbed can be estimated by using the very useful Remaining Concentration versus Carbon Dose plots that are independent of the initial concentration of the trace compound. Hybrid membrane processes and solids contact reactors provide a means for efficient adsorption of trace compounds. Data to be presented show that pulse addition of activated carbon to ultrafiltration systems (PAC-UF Process) yields more efficient use of the carbon than continuous addition, for example. Other data to be discussed show that the amount of trace compound adsorbed by carbon in solids contact reactors is significantly reduced by a strongly-competing fraction of NOM if the residence time of the carbon is too long.