The kinetics of adsorption determines how fast an adsorbate reaches equilibrium between activated carbon and water in drinking water treatment, and whether the capacities achieved in full-scale systems are mass-transfer limited. For a batch contactor (PAC), the kinetics of adsorption determines the dose and contact time required to reach effluent objectives. For a fixed-bed (GAC), the kinetics of adsorption determines the bed depth and contact time required to achieve a given percent removal. This study presents results for the effect of carbon dosage, temperature, and background organics on the rate of adsorption for atrazine at low initial concentrations (C. less than 10 ug/L). A homogeneous surface diffusion model (HSDM) is used to interpret the rate of adsorption, with experimentally determined adsorption isotherms as a boundary condition.