Adsorption of selenite (Se-3(2-)) on different polymorphic forms of iron oxyhydroxides and amorphous ferrihydrite was studied as a function of time, temperature, pH, and concentration of adsorbate(s) and adsorbent(s). Analysis of adsorption data indicates that the surfaces of all the forms of oxyhydroxides and ferrihydrite are heterogeneous in nature and that adsorption fits into a heterogeneous site binding model. The adsorption capacity of oxyhydroxides for SeO32- follows the order beta-FeOOH < alpha-FeOOH < gamma-FeOOH < delta-FeOOH < ferrihydrite.