Adsorption studies of Na(l), Cs(l), Ag(l), Tl(l), Co(ll), Sr(ll), Zn(ll), Cd(ll), Cu(ll), Pb(ll), Cr(lll), and Cr(VI) from aqueous solutions on activated carbons are reported. Most of the activated carbons used have been obtained from agricultural by-products (almond shells, olive stones, and peach stones). These activated carbons have been characterized using different techniques in order to know their textural characteristics (surface area and pore size distribution) and chemical nature. Some selected activated carbons have been treated to introduce oxygen and nitrogen surface complexes. The influence of different parameters such as: textural characteristics of activated carbons, chemical nature of the activated carbon surface, solution pH, and the presence of electrolytes in solution, on the metallic ions adsorption has been analyzed.